Circadian Disruption and Cancer: Making the Connection

Circadian Disruption and Cancer
Reported by
Megan Stephan

Posted August 24, 2009

Presented By

Jointly sponsored by the New York Academy of Sciences and the Mushett Family Foundation


The sharp delineation between day and night present through most of evolutionary history has been eroded in industrialized societies. Increasing nocturnal light and overnight shift work has coincided with a steady increase in incidence of cancer, prompting epidemiologists and other scientists to ask if there is a connection.

On June 19, 2009, researchers studying circadian rhythms and the physiological, biochemical, and molecular mechanisms behind them gathered at the New York Academy of Sciences to ponder this question and its implications for human health. Talks focused on three main areas: 1) evidence for the possible link between nighttime light and cancer risk, including the role of the hormone melatonin, which is the primary link between light perceived by the eyes and the internal circadian clock; 2) the molecular components of the circadian clock, and how they might interact with the pathways involved in cancer to promote or prevent it; and 3) how the development of cancer disrupts circadian rhythms in humans, and whether mitigation of this disruption could lead to better cancer treatment and outcomes.

The symposium was organized by William Hrushevsky of the University of South Carolina and David Blask of Tulane University School of Medicine.

Featured media

Russel J. Reiter

Keynote Address: Cancer, Circadian Disruption, Melatonin and the Clock

Russel J. Reiter (The University of Texas Health Science Center)

Use the tabs above to find a meeting report and multimedia on this event.

Speakers include:

Georg A. Bjarnason (Sunnybrook Odette Cancer Center) *
David E. Blask (Tulane University School of Medicine) *
Keith I. Block (Block Center for Integrative Cancer Treatment)
George C. Brainard (Jefferson Medical College)
Elisabeth Filipski (French Institute of Health and Medical Research) *
Steven M. Hill (Tulane Cancer Center) *
William J.M. Hrushesky (University of South Carolina School of Medicine) *
H. Phillip Koeffler (University of California, Los Angeles) *
Steven W. Lockley (Harvard Medical School) *
Russel J. Reiter (The University of Texas Health Science Center) *
Tyvin A. Rich (University of Virginia) *
Eva S. Schernhammer (Harvard Medical School) *
Richard Stevens (University of Connecticut Health Center) *
Patricia A. Wood (University of South Carolina) *
Xiaoming Yang (University of South Carolina) *

* Multimedia available


This conference has been made possible through the generous support of the Mushett Family Foundation. Click the sponsorship tab for a complete list of sponsors.

Circadian Phase Setting Effects of Melatonin in Free-living People

Steven W. Lockley (Harvard Medical School)
  • 00:01
    1. Introduction
  • 03:25
    2. Neuroanatomy of the circadian system; Melatonin rhythm
  • 08:14
    3. Circadian rhythm disorders and blindness; Melatonin as treatment; The phase response curve
  • 13:01
    4. Melatonin treatment studies
  • 16:04
    5. Breast cancer studies
  • 19:19
    6. Blind women and lower risk; Continuum of internal circadian desynchrony
  • 24:11
    7. Conclusion and acknowledgement

Circadian Rhythm in Rest and Activity

Georg A. Bjarnason (Sunnybrook Odette Cancer Center )
  • 00:01
    1. Introduction
  • 03:51
    2. Rest-activity monitoring in humans
  • 11:44
    3. The survival curve
  • 14:58
    4. Gender differences in rhythmic gene expression
  • 20:02
    5. Melatonin therapy in cancer patients
  • 23:41
    6. Conclusio

Cytokine-based Mechanisms by which Cancer Interferes with Circadian Organization

Tyvin A. Rich (University of Virginia)
  • 00:01
    1. Introduction; The sickness/behavioral model
  • 04:44
    2. Fatigue, cytokines, and cancer symptoms
  • 07:19
    3. Clustered systemic symptoms and circadian timing
  • 12:46
    4. Other lines of evidence
  • 16:10
    5. Radiation treatment and rest/activity cycles
  • 18:30
    6. Fatigue intervention study; Conclusio

Molecular Mechanisms of Melatonin's Anticancer Effects

Steven M. Hill (Tulane Cancer Center)
  • 00:01
    1. Introduction; Expression of the MT1 receptor
  • 04:47
    2. MT1 associated signaling pathways; ER-alpha phosphorylation
  • 08:31
    3. RAR-alpha transactivation assay
  • 10:21
    4. Melatonin and 9cRA; Invasion/metastasis in breast cancer
  • 15:04
    5. Melatonin and p38 MAPK; Melatonin and the MT1 receptor
  • 19:37
    6. The circadian clock and breast epithelial and cancer cells
  • 22:21
    7. Transcriptional activity in MCF-7 cells; SIRT1 and cancer
  • 27:08
    8. Summary and acknowledgement

Cancer, Circadian Disruption, Melatonin

Russel J. Reiter (The University of Texas Health Science Center)
  • 00:01
    1. Introduction; Physiological aspects of circadian rhythm
  • 11:05
    2. Melatonin
  • 13:45
    3. 24-hour rhythm and the consequences of disruption
  • 19:32
    4. Quantity of melatonin and darkness duration
  • 23:10
    5. Smith-Magenis syndrome; Jet lag
  • 29:25
    6. Per2; The inihibitory actions of melatonin on cancer
  • 32:51
    7. Key factors changed in cancer cells
  • 37:44
    8. Melatonin and MCF-7; Microfilaments and adhesion plaques
  • 42:56
    9. Contributing factors to oncostatic effects; Other effects of circadian disruption
  • 47:48
    10. Conclusio

Circadian Stage-dependent Metabolic and Anticancer Effects of Melatonin

David E. Blask (Tulane University School of Medicine)
  • 00:01
    1. Introduction
  • 03:50
    2. Linoleic acid, electric light, and cancer
  • 08:47
    3. Breast cancer; Rat studies
  • 20:04
    4. The effects of light intensity; Human studies
  • 26:27
    5. Prostate cancer; Summary and acknowledgement

Molecular Clock Mechanisms by which Circadian Disruption Causes Colon Cancer and Breast Cancer

Patricia A. Wood (University of South Carolina)
  • 00:01
    1. Introduction
  • 03:25
    2. Clock genes and cancer; Per2/Apc mouse study
  • 11:17
    3. Per2 mutation and beta-catenin signaling
  • 17:54
    4. The Apc mutation and abnormalities in clock function
  • 24:36
    5. Conclusions and acknowledgement

Circadian Time Dependent Tumor Suppression Function of Period Genes

Xiaoming Yang (University of South Carolina)
  • 00:01
    1. Introduction
  • 02:40
    2. Per1, Per2, and MTCL
  • 05:31
    3. Circadian rhythm and tumor growth rate; Clock controlled genes; shRNA
  • 08:07
    4. Down regulation of tumor Per1 and Per2; Circadian variation
  • 11:17
    5. Knockdown vs. control; Conclusion and acknowledgement

Abnormalities of Per2 in Lymphoid Malignancies

H. Phillip Koeffler (University of California, Los Angeles)
  • 00:01
    1. Introduction
  • 04:07
    2. C/EBP-inducible NIH 3T3 cells; Per2 expression
  • 10:42
    3. Per2 mRNA, C/EBP-alpha, and B-cell lymphoma
  • 13:23
    4. C/EBP-alpha and circadian clock gene expression; Summary and acknowledgement

Circadian Disruption in Advanced Lung Cancer

William J.M. Hrushesky (University of South Carolina School of Medicine)
  • 00:01
    1. Introduction; Measuring circadian organization
  • 03:46
    2. Sleep in lung cancer patients
  • 06:16
    3. Anxiety and depression
  • 09:05
    4. Quality of life
  • 11:35
    5. Summary, conclusions, and strategie

Circadian Disruption in Experimental Cancer Processes and Circadian Strategies for Improving Cancer Control

Elizabeth Filipski (French Institute of Health and Medical Research)
  • 00:01
    1. Introduction
  • 02:40
    2. Results of circadian disruption on mouse models
  • 13:53
    3. Experimental models to study the circadian timing system
  • 19:22
    4. Conclusions and perspective

Electric Light, Circadian Disruption, and Breast Cancer

Richard Stevens (University of Connecticut Health Center)
  • 00:01
    1. Introduction
  • 04:38
    2. Epidemiology
  • 08:04
    3. Light-at-night and breast cancer; IARC monographs
  • 11:47
    4. Genes and mechanisms
  • 17:38
    5. Cyclin D1; Circadian gene polymorphisms; Conclusio

Epidemiology of Circadian Disruption and Cancer Risk

Eva S. Schernhammer (Harvard Medical School)
  • 00:01
    1. Introduction
  • 04:29
    2. Factors influencing melatonin production
  • 10:15
    3. Cancer-inhibiting properties of melatonin; Shift work studies
  • 21:12
    4. Biomarker studies; Future directions; Shiftwork statistics
  • 25:34
    5. Preventive implications
  • 27:44
    6. Conclusion and acknowledgement

Web Sites

HHMI: Biological Clocks
Animations demonstrating the mechanisms of biological clocks in humans, all mammals, and the fruit fly Drosophila.

International Agency for Research on Cancer
Organization that coordinates and conducts research on the causes and mechanisms of human cancer and develops scientific strategies for cancer prevention and control.

International Dark Sky Association
Organization whose mission is to preserve and protect the nighttime environment through environmentally responsible outdoor lighting.

Journal of Biological Rhythms
Journal that publishes research into all aspects of biological rhythms, with emphasis on circadian and seasonal rhythms.

Journal of Circadian Rhythms
Journal that publishes research on all aspects of circadian and nycthemeral rhythms in living organisms.

Life Over Cancer
Website devoted to Keith Block's book, Life Over Cancer: The Block Center Program for Integrative Cancer Treatment.

Journal Articles

Additional Background

Stevens RG, Blask DE, Brainard GC, et al. 2007. Meeting report: the role of environmental lighting and circadian disruption in cancer and other diseases. Environ. Health Perspect. 115: 1357-1362.

Richard Stevens

Kloog I, Haim A, Stevens RG, et al. 2008. Light at night co-distributes with incident breast but not lung cancer in the female population of Israel. Chronobiol. Int. 25: 65-81.

Stevens RG. 2009. Electric light causes cancer? Surely you're joking, Mr. Stevens. Mutat Res. Jan 16. [Epub ahead of print]

Stevens RG. 2009. Light-at-night, circadian disruption and breast cancer: assessment of existing evidence. Int. J. Epidemiol. Apr 23. [Epub ahead of print]

Straif K, Baan R, Grosse Y, et al. 2007. Carcinogenicity of shift-work, painting, and fire-fighting. Lancet Oncol. 8: 1065-1066.

Eva S. Schernhammer

Schernhammer ES, Hankinson SE. 2009. Urinary melatonin levels and postmenopausal breast cancer risk in the Nurses' Health Study cohort. Cancer Epidemiol. Biomarkers Prev. 18: 74-79.

Viswanathan AN, Schernhammer ES. 2009. Circulating melatonin and the risk of breast and endometrial cancer in women. Cancer Lett. 281: 1-7.

Viswanathan AN, Hankinson SE, Schernhammer ES. 2007. Night shift work and the risk of endometrial cancer. Cancer Res. 67: 10618-10622. Full Text

George C. Brainard

Brainard GC, Sliney D, Hanifin JP, et al. 2008. Sensitivity of the human circadian system to short-wavelength (420-nm) light. J. Biol. Rhythms 23: 379-386.

Hanifin JP, Brainard GC. 2007. Photoreception for circadian, neuroendocrine, and neurobehavioral regulation. J. Physiol. Anthropol. 26: 87-94. (PDF, 90.4 KB) Full Text

Jasser SA, Hanifin JP, Rollag MD, Brainard GC. 2006. Dim light adaptation attenuates acute melatonin suppression in humans. J. Biol. Rhythms 21: 394-404.

Zaidi FH, Hull JT, Peirson SN, et al. 2007. Short-wavelength light sensitivity of circadian, pupillary, and visual awareness in humans lacking an outer retina. Curr. Biol. 17: 2122-2128.

Steven M. Hill

Lai L, Yuan L, Cheng Q, et al. 2008. Alteration of the MT1 melatonin receptor gene and its expression in primary human breast tumors and breast cancer cell lines. Breast Cancer Res Treat. Nov 4.

Lai L, Yuan L, Chen Q, et al. 2008. The Galphai and Galphaq proteins mediate the effects of melatonin on steroid/thyroid hormone receptor transcriptional activity and breast cancer cell proliferation. J. Pineal Res. 45: 476-488.

Xiang S, Coffelt SB, Mao L, et al. 2008. Period-2: a tumor suppressor gene in breast cancer. J. Circadian Rhythms 6: 4. Full Text

David E. Blask

Blask DE. 2009. Melatonin, sleep disturbance and cancer risk. Sleep Med. Rev. 13: 257-264.

Dauchy RT, Blask DE, Dauchy EM, et al. 2009. Antineoplastic effects of melatonin on a rare malignancy of mesenchymal origin: melatonin receptor-mediated inhibition of signal transduction, linoleic acid metabolism and growth in tissue-isolated human leiomyosarcoma xenografts. J. Pineal Res. May 22.

Dauchy RT, Dauchy EM, Davidson LK, et al. 2007. Inhibition of fatty acid transport and proliferative activity in tissue-isolated human squamous cell cancer xenografts perfused in situ with melatonin or eicosapentaenoic or conjugated linoleic acids. Comp. Med. 57: 377-382.

Patricia A. Wood and Xiaoming Yang

Wood PA, Yang X, Taber A, et al. 2008. Period 2 mutation accelerates ApcMin/+ tumorigenesis. Mol. Cancer Res. 6: 1786-1793.

Yang X, Wood PA, Ansell CM, et al. 2009. Beta-catenin induces beta-TrCP-mediated PER2 degradation altering circadian clock gene expression in intestinal mucosa of ApcMin/+ mice. J. Biochem. 145: 289-297.

Yang X, Wood PA, Oh EY, et al. 2008. Down regulation of circadian clock gene Period 2 accelerates breast cancer growth by altering its daily growth rhythm. Breast Cancer Res. Treat. Jul 24. [Epub ahead of print]

William J.M. Hrushesky

Du-Quiton J, Wood PA, Burch JB, et al. 2009. Actigraphic assessment of daily sleep-activity pattern abnormalities reflects self-assessed depression and anxiety in outpatients with advanced non-small cell lung cancer. Psychooncology Feb 6. [Epub ahead of print]

Levin RD, Daehler MA, Grutsch JF, et al. 2005. Circadian function in patients with advanced non-small-cell lung cancer. Br. J. Cancer 93: 1202-1208. (PDF, 116 KB) Full Text

Oh EY, Wood PA, Du-Quiton J, Hrushesky WJ. 2008. Seasonal modulation of post-resection breast cancer metastasis. Breast Cancer Res. Treat. 111: 219-228.

H. Phillip Koeffler

Gery S, Koeffler HP. 2007. The role of circadian regulation in cancer. Cold Spring Harb. Symp Quant. Biol. 72: 459-464.

Gery S, Virk RK, Chumakov K, et al. 2007. The clock gene Per2 links the circadian system to the estrogen receptor. Oncogene 26: 7916-7920.

Gery S, Gombart AF, Yi WS, et al. 2005. Transcription profiling of C/EBP targets identifies Per2 as a gene implicated in myeloid leukemia. Blood 106: 2827-2836. Full Text

Georg Bjarnason

Georg A. Bjarnason GA, Mackenzie RG, Nabid A, et al; National Cancer Institute of Canada Clinical Trials Group (HN3). 2009. Comparison of toxicity associated with early morning versus late afternoon radiotherapy in patients with head-and-neck cancer: a prospective randomized trial of the National Cancer Institute of Canada Clinical Trials Group (HN3). Int. J. Radiat. Oncol. Biol. Phys. 73: 166-172.

Innominato PF, Focan C, Gorlia T, et al; Chronotherapy Group of the European Organization for Research and Treament of Cancer. 2009. Circadian rhythm in rest and activity: a biological correlate of quality of life and a predictor of survival in patients with metastatic colorectal cancer. Cancer Res. 69: 4700-4707.

Tyvin A. Rich

Iurisci I, Rich T, Lévi F, et al. 2007. Relief of symptoms after gefitinib is associated with improvement of rest/activity rhythm in advanced lung cancer. J. Clin. Oncol. 25: e17-19.

Rich TA. 2007. Symptom clusters in cancer patients and their relation to EGFR ligand modulation of the circadian axis. J. Support Oncol. 5: 167-174; discussion 176-177.

Rich T, Innominato PF, Boerner J, et al. 2005. Elevated serum cytokines correlated with altered behavior, serum cortisol rhythm, and dampened 24-hour rest-activity patterns in patients with metastatic colorectal cancer. Clin. Cancer Res. 11: 1757-1764. Full Text

Steven W. Lockley

Flynn-Evans EE, Stevens RG, Tabandeh H, et al. 2009. Total visual blindness is protective against breast cancer. Cancer Causes Control. [Epub ahead of print]

Lockley SW, Dijk DJ, Kosti O, et al. 2008. Alertness, mood and performance rhythm disturbances associated with circadian sleep disorders in the blind. J. Sleep Res. 17: 207-216.

Lockley SW, Arendt J, Skene DJ. 2007. Visual impairment and circadian rhythm disorders. Dialogues Clin. Neurosci. 9: 301-314.

Zaidi FH, Hull JT, Peirson SN, et al. 2007. Short-wavelength light sensitivity of circadian, pupillary, and visual awareness in humans lacking an outer retina. Curr. Biol. Dec 17: 2122-2128.

Elizabeth Filipski

Filipski E, Innominato PF, Wu M, et al. 2005. Effects of light and food schedules on liver and tumor molecular clocks in mice. J. Natl. Cancer Inst. 97: 507-517.

Iurisci I, Filipski E, Reinhardt J, et al. 2006. Improved tumor control through circadian clock induction by Seliciclib, a cyclin-dependent kinase inhibitor. Cancer Res. 66: 10720-10728.

Lévi F, Filipski E, Iurisci I, et al. 2007. Cross-talks between circadian timing system and cell division cycle determine cancer biology and therapeutics. Cold Spring Harb. Symp. Quant. Biol. 72: 465-475.

Keith I. Block

Block KI, Gyllenhaal C, Tripathy D, et al. 2009. Survival impact of integrative cancer care in advanced metastatic breast cancer. Breast J. May 12. [Epub ahead of print]

Block KI, Jonas WB. 2006. "Top of the hierarchy" evidence for integrative medicine: what are the best strategies? Integr. Cancer Ther. 5: 277-281.

Block KI, Block P, Gyllenhaal C. 2004. The role of optimal healing environments in patients undergoing cancer treatment: clinical research protocol guidelines. J. Altern. Complement Med. 10 Suppl 1: S157-S170.

Russel J. Reiter

Erren TC, Reiter RJ. 2008. A generalized theory of carcinogenesis due to chronodisruption. Neuro. Endocrinol. Lett. 29: 815-821.

Korkmaz A, Reiter RJ. 2008. Epigenetic regulation: a new research area for melatonin? J. Pineal Res. 44: 41-44.

Reiter RJ, Tan DX, Korkmaz A, et al. 2007. Light at night, chronodisruption, melatonin suppression, and cancer risk: a review. Crit. Rev. Oncog. 13: 303-328.


David E. Blask, MD, PhD

Tulane University School of Medicine
e-mail | web site | publications

David Blask is professor and head of the Laboratory of Chrono-Neuroendocrine Oncology in the Department of Structural and Cellular Biology at Tulane. For the past 30 years, Blask's research has focused on the circadian control and therapeutics of cancer by melatonin as well as the consequences of the circadian disruption of melatonin production by light at night on cancer risk. He has published over 250 journal articles, reviews, chapters, and abstracts on this topic. His research has been supported by funding agencies such as the National Cancer Institute, National Institute of Child Health and Human Development, National Institute of Environmental Health Sciences, and the Edwin Pauley Foundation. He currently serves on the editorial boards of the Journal of Pineal Research, Neuroendocrinology Letters, and Integrative Cancer Therapies and is a consultant for the photobiology group of the International DarkSky Association. Blask has also served as a member of the working group on shift work for the International Agency for Cancer Research of the World Health Organization.

William J. M. Hrushesky, MD

University of South Carolina School of Medicine
e-mail | web site | publications

William Hrushesky is a senior clinician investigator at the WJB Dorn Department of Veterans Affairs Medical Center, a research professor at the University of South Carolina's School of Medicine's Department of Cell and Developmental Biology and Anatomy, and adjunct professor at the Norman J. Arnold School of Public Health's Department of Epidemiology and Biostatistics as well as the School of Computer Engineering's Department of Computer Science and Engineering, Columbia.

Hrushesky is a founder of Medical Chronotherapeutics (optimally timing medical preventatives, diagnostics, and treatments relative to rhythmic human biologic time structure). His research interests include the study of several important biological rhythms and especially of how these rhythms interact; drug delivery systems and particularly their temporal control; and solid tumor oncology. He is a medical expert in the care of patients with breast, lung, kidney, ovary, prostate, colorectal and head and neck cancer. To date, Hrushesky has mentored more than eighty physician scientists and scientists at all career levels. He has given several hundred invited lectures, and published over 700 scientific articles, chapters, or abstracts; holds several patents and is editor of several books and monographs. Current projects include: determining how the circadian clock within cancer cells orders proliferation, apoptosis and the expression of related therapeutic targets; determining the mechanisms by which surgical injury associated with primary tumor resection differentially impacts breast cancer dormancy depending upon the fertility cycle stage of that resection.

Kathy Granger, PhD

The New York Academy of Sciences
e-mail | web site

Kathy Granger manages the Life Science conferences at the New York Academy of Sciences. Granger received her PhD from the Department of Medicine, Monash University, Australia. She worked as a postdoctoral associate at Weill Cornell Medical College in New York City before joining the New York Academy of Sciences.

Keynote Speaker

Russel J. Reiter, PhD

The University of Texas Health Science Center
e-mail | web site | publications

Russel Reiter is professor in the Department of Cellular and Structural Biology at the University of Texas Health Science Center, San Antonio. Reiter's research interests relate to free radical aspects of disease processes and aging. Of particular interest is defining the role of oxygen derivatives in neurodegenerative diseases and their function in apoptosis, necrosis, and neuronal degeneration. Reiter's group is also investigating the free radical scavenging and antioxidant properties of pineal indoleamines, most notably melatonin. The investigations include the mechanisms of interaction of melatonin with free radicals and the resulting products. His group is also investigating the role of melatonin as a antitoxin against a variety of xenobiotics and environmental pollutants and the functional significance of melatonin and other indoleamines with processes of aging. Reiter is the editor-in-chief of the Journal of Pineal Research and on the editorial board of 7 other journals. He is the recipient of numerous awards including three honorary doctor of medicine degrees and, most recently, the Presidential Distinguished Scholar Award from UTHSCSA.


Georg A. Bjarnason, MD

Sunnybrook Odette Cancer Center, Toronto
e-mail | web site | publications

Georg Bjarnason is a senior scientist at the the Sunnybrook Odette Cancer Center in Toronto. His research focuses on the potential clinical applications of chronobiology and chronopharmacology in oncology. Bjarnson has shown that the timing of radiotherapy can impact the severity of oral mucositis in patients with head and neck cancer. Bjarnason is working to define the 24-hour variation of new cancer therapy targets both at the gene level and protein level in human tissue to allow for the design of intelligent clinical trials to optimize the effect and minimize the toxicity of these drugs. He is currently studying the expression of clock genes in cancer tissue, looking for both mutations and an abnormal circadian variation. Bjarnason is also conducting clinical trials using melatonin to normalize the circadian rhythm in patients with breast cancer and colorectal cancer.

Keith I. Block, MD

Block Center for Integrative Cancer Treatment
e-mail | web site | publications

Keith Block is an internationally recognized integrative cancer treatment specialist, researcher, and educator. A leader in laying the foundation for what is now called "integrative medicine," Block is medical/scientific director of the Block Center for Integrative Cancer Treatment and the Institute for Cancer Research and Education, which he and Penny B. Block, PhD, cofounded in 1980 in Evanston, Illinois. The Block Center uses research-based treatment methodologies that integrate the best of Western medicine with scientifically-sound complementary therapies. The focus is not only on eradication of disease, but on rebuilding biological integrity while honoring each person's psychosocial and spiritual needs.

Block is a member of the National Cancer Institute's Physician Data Query (PDQ) Cancer CAM Editorial Board, the editor-in-chief of the peer-reviewed journal Integrative Cancer Therapies, director of integrative medical education at the University of Illinois College of Medicine, adjunct assistant professor of pharmacognosy in the Department of Medicinal Chemistry and Pharmacognosy in the College of Pharmacy at the University of Illinois, and clinical assistant professor in the Department of Medical Education at the University of Illinois College of Medicine. In collaboration with the University of Illinois and other university facilities in the U.S. and Israel, Block conducts research in nutrition and in the use of natural medicines in cancer treatment.

George C. Brainard, PhD

Jefferson Medical College at Thomas Jefferson University
e-mail | web site | publications

George Brainard is a professor in the Departments of Neurology, Pharmacology, and Experimental Therapeutics at Jefferson Medical College of Thomas Jefferson University. He has directed Jefferson's Light Research Program since 1984. This program's research studies the effects of light on neuroendocrine physiology and circadian regulation in humans. Using the techniques of photobiology, radioimmunoassay, and performance testing, his group has documented how various visible and nonvisible light sources influence both hormonal balance and behavior. Current studies include elucidating the action spectrum of melatonin regulation, investigating the phase shifting capacities of light, studying the influence of light on tumor progression, and testing new light treatment devices for winter depression.

Elisabeth Filipski, PhD

French Institute of Health and Medical Research
e-mail | web site | publications

Elisabeth Filipski is a senior researcher at the French Institute of Health and Medical Research (INSERM), University of Paris, Paris. Her interests include the role of circadian timing system in cancer proliferation and in anticancer treatment activity. Her research aims at understanding the molecular and physiologic mechanisms of interactions between the circadian system, cancer growth, and drug pharmacology pathways in order to establish the experimental bases for personalized cancer chronotherapy. She was first to show that the suprachiasmatic nuclei, the hypothalamic circadian pacemaker, was a control point of tumor progression. She then identified the physiologic and molecular disruption brought about by chronic jet lag in experimental models and showed that such functional circadian disorder was responsible for malignant growth acceleration.

Steve M. Hill, PhD

Tulane Cancer Center
e-mail | web site | publications

Steve Hill is the Edmond & Lily Safra Chair for Breast Cancer Research Chairman of Structural and Cellular Biology (Anatomy), Tulane Cancer Center, New Orleans. His research focuses on understanding how hormones and factors cross-talk regulate breast cancer cell growth. Hill's laboratory has demonstrated that melatonin has significant inhibitory effects on the development and growth of human breast cancer. Furthermore, his studies have elucidated that melatonin can potentiate the actions of retinoic acid, a vitamin A derivative, to induce tumor cell death and prevent tumor formation. These studies are currently being moved into human clinical trials. Hill is a reviewer for a variety of journals including Cancer Research, Breast Cancer Research and Treatment, and Molecular Endocrinology and has served on NIH, DOD, and NSF grant review panels.

H. Phillip Koeffler, MD

University of California, Los Angeles
e-mail | web site | publications

H. Phillip Koeffler is the director of the Division of Hematology/Oncology at Cedars-Sinai Medical Center, Mark Goodson Chair in Oncology Research at Cedars-Sinai, hematologist/oncologist with the Cedars-Sinai Thyroid Cancer Center, and professor of medicine in the Division of Hematology/Oncology at the David Geffen School of Medicine at the University of California, Los Angeles (UCLA). Having developed a program in breast cancer research, Koeffler is looking at the molecular causes of the disease and researching novel forms of therapy.

He researches the basic biology of leukemias, preleukemias, and lymphomas, and is developing novel forms of therapy such as vaccines for these diseases. Koeffler has also developed a program in prostate cancer research and is looking at novel forms of therapy. He and his colleagues are also working to identify novel tumor suppressor genes using extensive tumor DNA banks from over twenty tumor types with matched normal control DNA from the same individual and over 300 microsatellites. Koeffler's group is sub-localizing the site of tumor suppressor genes that are mutated in a variety of cancers. Koeffler is a member of editorial boards for numerous peer-reviewed journals, including Cancer Research, the International Journal of Oncology, Journal of Molecular Medicine, Cytokines and Molecular Biology, Leukemia, Cancer Molecular Biology, Leukemia Research, and Hematologic Pathology.

Steve Lockley, PhD

Harvard Medical School
e-mail | web site | publications

Steve Lockley is an assistant professor of Medicine at Harvard Medical School and an associate neuroscientist in the Division of Sleep Medicine, Department of Medicine at Brigham and Women's Hospital, Boston. Lockley's research focuses on basic and applied aspects of human circadian biology, using epidemiology, field-based physiological studies, and inpatient intensive physiological monitoring. He has a particular interest in human circadian photoreception and the effects of light on the circadian pacemaker and other non-image forming responses. Lockley's studies include investigations of the effects of timing, duration, intensity and wavelength of light exposure on circadian resetting, melatonin suppression, and the acute alerting effects of light.

He also studies visually impaired individuals to examine the effects of the severity and type of blindness on circadian photoreception, the periodicity of the circadian pacemaker and development of circadian rhythm sleep disorders. These basic studies have led to the development of novel therapeutic strategies to treat sleep disorders with melatonin administration in blind patients. He examines the role of visual impairment on endocrinology and breast cancer risk in blind women. With the Harvard Work Hours Health and Safety Group, Lockley's group assesses the impact of extended work hours on health and safety of workers and the public, including the development of interventions in hospital residents, and the implementation of large-scale occupational fatigue management and sleep disorders screening programs in several police forces nationwide.

Tyvin Rich, MD

University of Virginia
e-mail | web site | publications

Tyvin Rich is a professor of radiation oncology at the University of Virginia, Charlottesville. The Rich laboratory studies the molecular mechanisms behind the fatigue that cancer causes. Their laboratory findings support the hypotheses that tumors can produced neurally active peptides (cytokines) that are capable of altering output of the biologic clock. The clinical application of their observations may be to help understand the causes and how to intervene more effectively in patients suffering with symptoms of cancer induced fatigue.

Eva Schernhammer, MD, DrPH

Harvard Medical School
e-mail | web site | publications

Eva Schernhammer is an assistant professor of medicine at Harvard Medical School and an assistant professor of epidemiology in the Department of Epidemiology at the Harvard School of Public Health. Schernhammer's research interest is in exploring the exposures that influence the circadian system in humans and health consequences. She has done work on the effects of light at night on cancer risk through the melatonin pathway and demonstrated that the effects of light at night may affect not only breast cancer, but also other cancers such as colorectal cancer, generating evidence that supports a new hypothesis on the development of cancer. She has also conducted urinary melatonin measurements in the Nurses' Health Study to assess the hormone's variations according to shift work status and its association with breast cancer risk in the Nurses' Health Study. Current projects study the role of clock genes in these associations and melatonin's cancer preventive potential.

Richard G. Stevens, PhD

University of Connecticut Health Center
e-mail | web site | publications

Richard Stevens is a professor and cancer epidemiologist in the Division of Epidemiology & Biostatistics, Department of Community Medicine and Health Care, University of Connecticut Health Center, Farmington. Stevens's research focuses on the etiology of cancer. One of his major interests has been in the possible role of iron overload. Largely on the basis of his work, published in the Journal of National Cancer Institute and the New England Journal of Medicine, the Swedish food industry decided to cease iron fortification of flour in the early 1990s. A perplexing challenge, which Stevens began to engage in the late 1970s, is the confounding mystery of why breast cancer risk rises so dramatically as societies industrialize. He proposed in 1987 a radical new theory that use of electric lighting, resulting in lighted nights, might produce "circadian disruption" causing changes in the hormones relevant to breast cancer risk. Accumulating evidence has generally supported the idea, and it has received wide scientific and public attention. For example, his work has been featured on the covers of the popular weekly Science News (October 17, 1998) and the scientific journal Cancer Research (July 15, 1996).

Patricia A. Wood, MD, PhD

University of South Carolina
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Patricia Wood is an associate professor of Internal Medicine and Pathology at the USC School of Medicine and chief of the Oncology/Hematology Division at the Dorn VA Medical Center, Columbia. Dr. Wood's research has included studies of membrane protein and biochemical changes associated with the erythrocyte stage of malaria infection and changes with resistance to anti-malarial drugs; pre-clinical and clinical anti-cancer drug toxicity and efficacy studies; clinical cancer treatment trials through NCI, pharmaceutical and local institutional sponsored programs; and investigations of the effects of biologic rhythms, such as daily (circadian) rhythms and fertility cycle rhythms, on the balance between host and cancer in pre-clinical and clinical settings. She is the recipient of the American Cancer Society Career Development Award, Department of Veterans Affairs RAG and MERIT Review funding and National Institutes of Health research funding.

Xiaoming Yang, PhD

University of South Carolina
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Xiaoming Yang is a postdoctoral fellow in the Chronobiology and Oncology Research Laboratory at the University of South Carolina, Dorn VA Medical Center, Columbia. The focus of the ongoing research in the laboratory is the effect of biologic rhythms upon host cancer balance, tumor biology, and the efficacy and toxicity of cytotoxic drugs and growth factors used in hematology and oncology. The biologic rhythms of interest include the circadian (~24 hour, daily) and fertility (estrous, menstrual) cycles and seasonal rhythms.

Megan Stephan

Megan Stephan studied transporters and ion channels at Yale University for nearly two decades before giving up the pipettor for the pen. She specializes in covering research at the interface between biology, chemistry and physics. Her work has appeared in The Scientist and Yale Medicine. Stephan holds a PhD in biology from Boston University.

Can the increased cancer risks of shift workers be reduced using therapies such as melatonin supplementation to promote more robust circadian rhythms?

Could the reduction of light pollution lead to lower cancer rates in industrialized societies?

Will the proteins that constitute the circadian clock represent good targets for intervention in cancer?

What is the role of tumor-specific circadian rhythms in the development and progression of cancer?

Why are circadian gene expression patterns so different between men and women?

Will paying greater attention to the role of circadian rhythms in quality of life parameters for cancer patients lead to better treatment outcomes?

Until quite recently in evolutionary history, night was a time of darkness, varied only by the presence of a full moon or when clouds obscured the stars. Daytime was, by contrast, a period of much greater brightness. Humans, animals, and even unicellular organisms developed circadian rhythms that let them follow this day/night, light/dark pattern very closely, prompting them to be active during the day and sleep at night, or vice versa, depending on their affinity for a nocturnal, diurnal, or other type of lifestyle.

With Edison's invention of the light bulb, however, the sharp delineation between day and night ended in industrialized societies. Humans are now often exposed to quite high levels of light at night, whether through light pollution, because they are awake longer in the evening, or because they must stay awake to work the night shift. At the same time, daytime exposure to light has decreased as more workers stay indoors in often poorly lit environments. Coinciding with the rise of light at night, industrialized countries have seen a steady increase in the incidence of cancer, prompting epidemiologists and other scientists to ask if there is a connection between exposure to light at night and the development of cancer.

On June 19, 2009, a group of researchers studying circadian rhythms and the physiological, biochemical, and molecular mechanisms behind them gathered at the New York Academy of Sciences to ponder this question and its implications for human health. The symposium was organized by William Hrushevsky of the University of South Carolina and David Blask of Tulane University School of Medicine.

A bright new world

The first session examined evidence for the possible link between light at night and cancer risk and the role of the hormone melatonin, which is the primary link between light perceived by the eyes and the internal circadian clock. Epidemiologists Richard Stevens of the University of Connecticut Health Center and Eva Schernhammer of Harvard Medical School described a large body of research linking light exposure at night, particularly among shift workers, to increased cancer risk, including often hormonally driven cancers such as breast and prostate. George Brainard of Jefferson Medical College described his work on the physiological and biophysical aspects of light transmission through the eye and the effects of light at night on melatonin production in humans. Steve Hill of Tulane Cancer Center presented work on the melatonin receptor, MT-1, and its role in modulating cell signaling pathways that are also known to be involved in cancer. David Blask described metabolic rhythms that are tied to melatonin levels, and that implicate consumption of the fatty acid linoleic acid, commonly found in so-called junk foods like potato chips and pastries, in the mechanisms of cancer development.

In the second session, researchers presented work on the molecular components of the circadian clock, and how they might interact with the pathways involved in cancer to promote or prevent it. Much of this work focuses on the role of the Period genes (abbreviated Per) which produce the key clock proteins PER1 and PER2. Patricia Wood of the University of South Carolina described her work on the interactions between Per gene mutations and mutations of the Apc gene of mice, which work together to promote the development of cancerous polyps in the small intestine and colon. Xiaoming Yang, also of the University of South Carolina, discussed his work comparing the rhythmic patterns of PER1 and PER2 expression in normal tissues with those in tumors, investigating the molecular basis for the strong circadian rhythms observed in tumor growth rates. H. Phillip Koeffler of the University of California, Los Angeles, described work linking Per mutations to certain types of hematologic malignancies, including acute myelogenous leukemia and diffuse large B-cell lymphoma.

The third session examined the link between circadian rhythms and cancer from the completely opposite perspective, as researchers explored how the development of cancer leads to the disruption of circadian rhythms in humans, and whether mitigation of this disruption could lead to better cancer treatment and outcomes. William Hrushesky described his ongoing studies of the effects of circadian rhythm disruption on advanced lung cancer patients. Georg Bjarnason, of the Toronto-Sunnybrook Regional Cancer Center, presented work in colorectal patients which has led to enhanced awareness of gender differences in the genes and proteins whose expression is controlled by the circadian clock. Tyvin Rich of the University of Virginia discussed his work on the connection between the greatly increased expression of cytokines in cancer patients and circadian disruptions. Elisabeth Filipski of the French Institute of Health and Medical Research described her work using mouse models of disrupted circadian rhythm to explore effects on tumor growth in different cancer types. Keith Block provided information on his Center for Integrative Cancer Treatment, which combines interventions intended to restore circadian rhythms with a wide array of other pharmacological and non-pharmacological interventions to improve cancer treatment.

The keynote address, given by Russ Reiter of the University of Texas Health Science Center, San Antonio, pulled much of this research together from the perspective of a pioneer in the field of melatonin research. Reiter spoke for many in saying that the weight of accumulated evidence strongly suggests that the disruption of circadian rhythms is a major factor in cancer and perhaps other diseases as well. Reiter said that "repeated perturbations of these systems has biological consequences," or, in other words, "there is a price to pay" for disrupting the work of these ancient regulatory systems in our bodies.

Richard Stevens, University of Connecticut Health Center
Eva Schernhammer, Harvard Medical School
George Brainard, Jefferson Medical College at Thomas Jefferson University
Steve Hill, Tulane Cancer Center
David Blask, Tulane University School of Medicine


  • Different clocks control circadian rhythms that operate on an organismal versus the cellular level.
  • There is growing evidence that disrupted circadian rhythms increases cancer risk.
  • Higher melatonin levels were associated with a 41% reduction in the risk of breast cancer in the second Nurses' Health Study.
  • Very low levels of light are needed to affect human melatonin production.
  • Uptake of linoleic acid, a fatty acid whose metabolite increases cell proliferation, is regulated by melatonin.

The rhythms of life

In humans, the central biologic clock is a region in the anterior hypothalamus of the brain known as the suprachiasmatic nucleus (SCN). This region controls multiple circadian rhythms at the organismal level, including behavioral rhythms such as sleep, hunger, and thirst, and physiological rhythms such as blood pressure, body temperature, and hormone production. But this is not the only clock that is present in humans. The clock mechanism itself, which consists of a complex cycle of gene–gene and gene–protein interactions, is found in many cells in the body, where it governs rhythms that are specific to the functions of different cells and tissue types. Tissues such as the lungs, liver, pancreas, spleen, thymus, and skin have all been shown to produce cyclical patterns of gene expression that follow a circadian rhythm.

Light entrains the biologic clock.

The human circadian clock is entrained to the day/night cycle by the amount and type of light that reaches special receptor cells in the retina of the eye. These cells form part of a sensory system for light that is completely separate from the one that is responsible for vision. In the absence of light, these cells send a message to the pineal gland, also located in the brain, to produce the hormone melatonin. Melatonin is the biologic indicator of darkness: its production peaks during the night and is low during the day. Humans who are exposed to light at night produce less melatonin, and thus may have disrupted circadian rhythms.

The melatonin factor

Richard Stevens of the University of Connecticut Health Center recounted much of the epidemiologic evidence that links the disruption of circadian rhythms to the development of cancer. He noted that the incidence of breast cancer continues to rise around the world, and is especially high in the U.S. and Western Europe. Decades of intensive research have failed to confirm the once popular hypothesis that a high fat diet is responsible for this increase. Melatonin reduces the production of reproductive hormones such as estrogen and progesterone, which led to the hypothesis that at least some of the increased cancer risk in industrialized societies, particularly for hormonally driven cancers like breast and prostate, is due to light at night and the consequent reduction in circulating melatonin levels.

This hypothesis makes a number of predictions, including that shift workers would be at higher risk of breast cancer, and that profoundly blind women would be at lower risk. Multiple epidemiologic studies have shown that these predictions are correct, and have uncovered a link between light at night and prostate cancer as well. The evidence is compelling enough that the International Agency for Research on Cancer (IARC) concluded in a 2007 review article that "shift work that involves circadian disruption is probably carcinogenic in humans." Stevens also reviewed recent genetic studies of the association between circadian clock gene polymorphisms and the risk of developing cancer. He said that multiple such associations have been found but thus far they have been modest in magnitude, and it is not yet known if they are replicable between studies.

Eva Schernhammer of Harvard Medical School is a researcher involved in the Nurses' Health Study, which consists of two long-term prospective studies of women's health that have produced key evidence for the link between circadian rhythm disruptions and cancer. Schernhammer described how melatonin levels vary among individuals, based on factors such as age, diet, body mass index (BMI), lack of sleep, or the need to be awake at night due to shiftwork. Studies have shown that people who work the night shift have lower levels of melatonin. Melatonin has a number of possible roles in cancer prevention: it may act as an antioxidant, as an immunomodulator, or it may reduce the levels of reproductive hormones. Reduced melatonin levels may also affect the expression of multiple other chemical messengers, in turn leading to increased risk for many different types of cancers.

In the Nurses' Health Study, shift workers had a 36%–79% increased risk of breast cancer.

The Nurses' Health Study included two prospective cohort studies, one beginning in 1976 and the other in 1989, for a total of around 250,000 women. When the data were adjusted for BMI, alcohol intake, and exercise levels, these studies showed that shift workers had a 36%–79% increased risk of breast cancer. Shift workers also had a 35% increase in the risk of colorectal cancer and a 43% increase in the risk of endometrial cancer. The 1989 study also showed that higher melatonin levels were associated with a 41% reduction in the risk of breast cancer. Many of these findings have been confirmed and extended by other studies.

Schernhammer said that it is estimated that 15 million Americans work night shifts. More African Americans work night shifts than whites, and most are men, except in certain professions such as nursing. Protecting the health of these workers is an important public health problem. At this time, it is unknown whether interventions such as melatonin supplementation or providing special light conditions are safe and would reduce cancer risks. It is also unknown whether there is a specific time of life when humans are more vulnerable to cancers caused by light at night, or whether changes such as limiting the number of years on the night shift might mitigate risks. These are topics of future research in this area.

George Brainard of Jefferson Medical College at Thomas Jefferson University presented his work on the characteristics of light transmission by the eye and how they are related to melatonin production in humans. He and his group are examining multiple aspects of ocular physiology, including behavioral characteristics such as gaze, physical characteristics of the lens and pupil, and the location and sensitivity of photoreceptors responsible for melatonin regulation.

Brainard described highly detailed studies intended to uncover how much light and which part of the light spectrum is most important for inhibiting melatonin production. Human subjects were exposed to monochromatic light during the night under very controlled conditions and their melatonin levels measured. The researchers found that melatonin production is reduced most by light in the blue region of the spectrum, compared to the visual system for which responses peak in the yellow to green region. They also found that only very low levels of light are needed to affect human melatonin production. Their findings could have important implications for understanding how light exposure in the real world affects melatonin production, how light at night might affect human health, and how these effects might best be mitigated.

Molecular mechanisms

Steve Hill of the Tulane Cancer Center is investigating the molecular mechanisms that might link melatonin to the prevention or treatment of cancer. In vitro, melatonin has been shown to have direct effects on cancer cells—for example, suppressing the growth and proliferation of breast cancer cells in an effect that is mediated by the melatonin receptor, MT-1. Hill and his group have found that a portion of the MT-1 receptor population is localized to lipid rafts, cell membrane platforms that form gathering places for important signaling molecules, including many of the receptors and kinases involved in cancer. They are working to identify and trace specific signaling pathways that might link MT-1 to cancer, including well known pathways that are aberrant in cancer such as Raf, ERK/MEK, and AKT. The estrogen receptor, whose activity promotes the growth of many breast cancers, is modulated by the activities of many of these pathways.

Hill and his group have found that melatonin reduces the expression of estrogen receptor-α, and also modulates the expression of a variety of other nuclear and/or steroid hormone receptors. These results and others led Hill to test 9-cis-retinoic acid, a ligand of the nuclear retinoid X receptors (RXRs), in combination with melatonin as a treatment for carcinogen-induced tumor formation in rats. RXRs are thought to be involved in the regulation of a large number of metabolic and developmental pathways, many of which are implicated in cancer. The 9-cis-retinoic acid/melatonin combination reduced tumor incidence from 90% to 5%–12%, and also induced complete or partial tumor regression in many cases. The overall response rate to this treatment was 98% if tumor stasis was also taken into account, suggesting a high potential payoff for therapies based on this approach.

The activity of melatonin, the melatonin receptor, and clock genes suggest many potential drug targets against cancer.

Hill and his group are pursuing many other aspects of the melatonin–cancer link. They found that melatonin also appears to play a role in tumor invasion and metastasis, a role that is mediated by the p38 MAP kinase signaling pathway and whose downstream effects may be on the expression of matrix metalloproteases, which are important for tissue invasion. They are also investigating the roles of clock genes such as Per2, Cry2, and Sirt1 in the control of cell proliferation, cell cycle, and apoptosis in breast cancer cells. Their research has identified many points at which melatonin, the melatonin receptor, and/or clock genes could be involved in cancer initiation, promotion, and progression, suggesting multiple new targets for drugs that might prevent or treat primary cancers or metastases.

David Blask and his group at the Tulane University School of Medicine are interested in the interactions between light, circadian timing disruption, and diet in the development of cancer. They have focused on the role of linoleic acid, which is the most common fatty acid in our diets. Linoleic acid consumption has risen at the same time as the use of electric light has increased. This fatty acid provides an excellent source of caloric energy for cancers to use as they increase their biomass, and also plays an important signaling role in cell proliferation.

At the cellular level, uptake of linoleic acid is initiated by activation of the protein kinase A (PKA) signaling pathway. Once it enters the cell, a metabolite of linoleic acid, known as 13-HODE, participates in further signaling pathways that promote cell proliferation. Melatonin downregulates PKA, thus reducing linoleic acid uptake and inhibiting these growth-promoting pathways. This phenomenon has been shown to occur in human breast, head and neck, and urogenital cancers.

Blask and his group are investigating the details of this phenomenon by studying the influence of light on human breast cancer xenografts grown in nude mice, which lack intact immune systems and are unable to reject foreign tissue. If the mice are kept on a regular light/dark schedule, linoleic acid uptake and 13-HODE production are rhythmic in the tumors, peaking late in the day. But if the mice are exposed to light at night, this rhythm is lost and these levels stay high all of the time. Tumor growth rates were also found to be rhythmic. The tumors still grew in the presence of an intact light/dark cycle, but growth rates were dramatically increased when this cycle was disrupted or absent. The investigators are working to confirm these findings in humans, and to extend them to other cancers, including prostate.

William Hrushesky, University of South Carolina
Georg Bjarnason, Sunnybrook Odette Cancer Center, Toronto
Tyvin Rich, University of Virginia
Steve Lockley, Harvard Medical School
Elisabeth Filipski, French Institute of Health and Medical Research
Keith Block, Block Center for Integrative Cancer Treatment
Russel Reiter, The University of Texas Health Science Center


  • Lung cancer patients with higher levels of circadian disruption showed higher rates of anxiety and depression and scored lower on quality of life indices.
  • There are large differences in rhythmic gene expression in men versus women.
  • Administration of melatonin can help blind people entrain to the day/night cycle, and thus may also be useful in regulating the circadian rhythms of individuals with cancer.
  • Cytokines can affect the SCN and the high levels produced in disease situations may cause the mood and sleep disorders associated with them.
  • Meal timing can induce stable circadian rhythms in mice without an SCN, suggesting that behavioral approaches may also promote more stable rhythms in cancer patients.
  • Holistic approaches that include consideration of circadian rhythms may improve the effectiveness and tolerability of cancer treatment.
  • Melatonin has many overlapping actions in addition to clock entrainment, including roles in the immune system and as an antioxidant.

Improving quality of life

In addition to arising from circadian disruptions, cancer and cancer treatments frequently cause circadian disruptions, leading to a greatly reduced quality of life for many cancer patients. Many patients, particular those with advanced cancer, suffer from poor sleep at night, daytime fatigue, reduced appetite, muscle wasting, reduced mental and physical functioning, anxiety, depression, and other debilitating symptoms. Many researchers believe that treating circadian disruption in these patients will improve their quality of life and may also lead to improved survival.

William Hrushesky initiated the discussion of this topic with a description of his clinical studies that are intended to improve the last year of life for patients with advanced lung cancer. Previous studies in colorectal cancer showed that many patients had increased levels of nocturnal activity and daytime sleeping, and that higher levels of circadian disruption were associated with reduced survival rates. Hrushesky and his group are in the initial stages of a study to investigate whether the same holds true for patients with lung cancer, and whether interventions that improve circadian rhythm can improve quality of life and survival rates for these patients.

He and his group have designed a research program that combines objective monitoring of patient activity by actigraphy with more subjective tools, such as patient questionnaires, that ask about quality of life, fatigue, anxiety and depression, sleep habits, and other potentially related symptoms. This wide array of research tools was used to assess the degree to which circadian rhythms were disrupted in 84 lung cancer patients, half of whom were hospitalized and half of whom were at home. Completion of these baseline assessments showed that most of these patients slept very badly, particularly when they were in the hospital, and that patients whose sleep patterns showed higher levels of circadian disruption also showed higher rates of anxiety and depression and scored lower on quality of life indices.

Lung cancer patients, especially those in the hospital have much worse scores on the Pittsburg Sleep Quality Index (PSQI), which measures seven components related to sleep.

These assessments have validated circadian disruption as an important therapeutic target in advanced lung cancer patients. Further studies will assess the effects of interventions intended to improve circadian rhythm, which may include exercise, exposure to full spectrum light at certain times of the day, optimization of sleep hygiene, melatonin supplementation, and others.

Georg Bjarnason of the Sunnybrook Odette Cancer Center in Toronto is investigating the role of circadian rhythm in the success of colorectal cancer treatment. He and his collaborators compared the effect of giving colorectal cancer patients a well known treatment regimen, known as FOLFOX, at undefined times, with the same treatment regimen optimized for circadian timing, known as ChronoFLOX. While they found no difference in survival for the ChronoFLOX treated group as a whole, they found that this treatment dramatically improved survival in men but had the opposite effect in women, even though the men and women had no major differences in their sleep/activity patterns.

The expression patterns of most rhythmic genes differ between men and women.

Bjarnason and his group are investigating the biological basis for this phenomenon by examining genomic and proteomic differences between men and women in the expression of rhythmic genes. They have found that out of about 2000 rhythmic genes, only 200 were expressed in patterns that overlapped between men and women. Other investigators have found that about half of rhythmically expressed proteins were associated with RNAs that were not rhythmically expressed. These findings suggest that there is still much to be learned about when and how the circadian clock controls gene and protein expression, and how that control is affected by gender.

Bjarnason and his group are also looking at the differences in rhythmically expressed genes between cancer cells from male and female patients. These findings have important implications for drug development because drug candidates are often tested in cell cultures, which do not have circadian rhythms, or in rats and mice, which are nocturnal and are likely to have very different patterns of gene expression at the time of day when they receive the experimental agents compared with humans, who are diurnal.

The development of cancer is often accompanied by a cytokine storm, that is, greatly increased levels of a wide range of immunological and inflammatory messenger molecules, resulting in the disruption of normal physiological functioning. Tyvin Rich of the University of Virginia is studying the effects of this storm and its relationship to the disruption of circadian rhythm in cancer patients. High levels of cytokines and other immunomodulatory molecules can result in pain, increased drug toxicity and resistance, psychobehavioral changes, and other symptoms, and may promote cancer recurrence and progression as well. Rich suggested that the effects of these cytokines on the SCN, which contains cytokine receptors, may explain the clustering of common cancer symptoms such as fatigue, depression, and loss of appetite.

He and his group are studying the relationship of fatigue and other quality of life indicators to serum levels of cytokines in cancer patients with a wide range of tumor types. Their studies have shown that in general, cancer patients have higher levels of the cytokines IL-6 and IL-8 than normal controls. However, patients in their study who had more robust circadian rhythms had lower levels of IL-6, as well as less fatigue and loss of appetite. Patients whose circadian rhythms were disrupted had the opposite characteristics. The researchers also found that patients with disrupted rhythms had elevated levels of EGFR ligands and VEGF in their blood, a finding that has important implications for the use of targeted cancer therapies that depend on blocking the receptors for these molecules.

The success of interventions to promote more robust circadian rhythms in cancer patients depends on a good understanding of these rhythms and how they are entrained by exposure to melatonin and light. Steve Lockley of Harvard Medical School shared his expertise on melatonin cycles in humans and how to use melatonin supplementation and/or light therapy most effectively.

Lockley noted that melatonin secretion does not require periods of light and darkness to be rhythmic, but that these signals are what entrains the internal clock to the external day/night cycle. Blind people often produce melatonin in a rhythmic pattern, but because their cycles are usually more or less than 24 hours their rhythm drifts away from the actual day/night cycle. This drift can be treated with melatonin, which when given at the appropriate time can either advance or delay the cycle as needed. Giving exogenous melatonin changes the time of the melatonin peak and thus promotes sleep at night when it is more appropriate. Melatonin given in the early evening advances the clock, while melatonin given in the morning delays the clock. In cancer patients who are sighted, light could also be used similarly to advance or delay the clock and promote more robust rhythms.

Lockley described a study of 1367 blind women from the U.S. and Canada who had varying degrees of light perception. They found that profoundly blind women, who had no light perception at all, had about half the risk of breast cancer of blind women with some residual light perception, after adjustment for other factors including reproductive parameters such as exposure to estrogen. Increased estrogen exposure is a known risk factor for breast cancer. Their study also showed that profoundly blind girls tended to reach menarche earlier, and thus are exposed to more estrogen over the course of their lives, yet their risk of breast cancer was still lower than in women with some light perception. Lockley and his group are working to better understand the relationship between light perception, melatonin levels, and estrogen exposure as they relate to breast cancer risk.

Breast cancer risk is associated with suppressed melatonin levels and disrupted melatonin rhythms.

There are many potential benefits to using light or melatonin therapy to stabilize circadian rhythms in blind people, cancer patients, or other populations. Such interventions can standardize sleep-wake timing with the rest of society, improve mood and alertness, and make other changes in quality of life parameters. Lockley also suggested that a stabilized cycle might be valuable in cancer patients by allowing health care providers to match the patient's clock to optimal treatment times.

Alterations in daily rhythms of rest-activity or in blood levels of the hormone cortisol have been shown to predict poor survival in patients with metastatic colorectal, metastatic breast, and early stage lung cancer. Elisabeth Filipski of the French Institute of Health and Medical Research is studying this phenomenon in a number of experimental mouse models. Circadian rhythms can be disrupted in mice using a variety of methods, including destruction of the SCN, introducing clock mutations, or providing unevenly varying patterns of light and darkness that put mice in a state resembling chronic jet lag. Filipski is using these models to investigate the connections between tumor growth and circadian disruption.

Enhancing the circadian clock in peripheral tissues, including the tumor itself, may have beneficial effects.

She and her group have shown that mice whose SCNs have been ablated show faster growth in at least two types of tumors, Glasgow osteosarcoma and pancreatic adenocarcinoma. Mice with chronic jet lag show changes in clock gene expression in their livers, and tumors in their livers grow faster. Filipski has also shown that meal timing can be used to entrain mice whose SCNs are ablated back to a stable rhythm, reducing tumor growth rates. This type of circadian reinforcement also reduced tumor growth rates in mice with chronic jet lag. These results suggest that enhancement of the clock in peripheral tissues, including the tumor itself, may have beneficial effects that are just as important as reinforcing the rhythm of the central clock.

Keith Block of the Block Center for Integrative Cancer Treatment, Chicago, rounded out the session by describing his efforts to include treatment for circadian disruption into an integrative model of cancer treatment that also includes diet and lifestyle interventions; treatment to improve biological factors such as oxidative stress, inflammation, and immune disruptions; and treatment of the pathological aspects of cancer. This approach includes multiple interventions that are intended to produce and maintain circadian integrity, both as a means of improving quality of life and potentially improving the odds for survival.

Block described how quality of life issues such as fatigue, insomnia, constipation, and lack of appetite can be related to biochemical disruptions, such as changes in inflammation, growth factors, and immune status, and clinical complications, such as appetite suppression, muscle wasting, pneumonia, headache or pain. These symptoms may exacerbate treatment side effects and sometimes even prevent appropriate treatment from being administered. Such issues may lead to the recurrence or progression of cancer, or to more serious, life-threatening complications that might otherwise have been avoided. Additionally, research demonstrates that patients who are unable to maintain optimal chemotherapy dosing, suffer from interrupted treatment scheduling, or are simply unable to complete a full course of treatment, face poorer response and shorter survival. Thus health status and other factors impacting quality of life issues can be directly related to patient survival.

Many of these issues can be addressed by minimizing circadian disruption and prescribing therapies to reset a patient's clock. Block and his coworkers have designed an individualized program that assesses quality of life and circadian disruptions and addresses as many issues as possible for each cancer patient. Their program includes not only change in the content of diet but also when particular foods are to be eaten. Exercise is used to promote better rest-activity cycling as well as nutritional supplements, and pharmacological interventions are given according to available research on the best times of day for such treatment. Preliminary research on a cohort of 90 metastatic breast cancer patients (Breast Journal, July 2009) demonstrates favorable outcome. Time will tell if this holistic approach is replicable and produces better outcomes for patients treated at the center.

In a final session, keynote speaker Russ Reiter of the University of Texas Health Science Center, considered the father of pineal gland and melatonin research, provided an evolutionary perspective on melatonin and tied together many of the topics of the day. He said that melatonin is 2.5 to 3 billion years old and is found in bacteria, birds, reptiles, and insects in addition to mammals. Melatonin is produced in other tissues besides the pineal gland in mammals, including the female ovary and the retina, but only the pineal gland releases it into the rest of the body to provide central clock regulation. He noted that melatonin has many overlapping actions in addition to clock entrainment, including roles in the immune system and as an antioxidant.

Humans living in industrialized society are melatonin-deficient, he said, because they are exposed to less darkness. Given melatonin's many roles, it is not hard to imagine that the disruption of circadian rhythms may be source of many of the disorders of modern life, including not only cancer but also diabetes and obesity, depression, and other disorders as well.

Patricia Wood, University of South Carolina
Xiaoming Yang, University of South Carolina
H. Phillip Koeffler, University of California, Los Angeles
William Hrushesky, University of South Carolina


  • Mice with mutations in the circadian clock gene Per2 develop tumors that are resistant to radiation-induced apoptosis.
  • The PER2 protein may act as a tumor suppressor by regulating the beta-catenin signaling pathway.
  • Tumors appear to have their own internal clocks.
  • Per2 gene expression is regulated by the C/EBP family of transcription factors.


The operation of the circadian clock itself and the mechanisms by which changes in clock genes and proteins could be involved in causing cancer or promoting its growth are topics of intense investigation. Patricia Wood of the University of South Carolina described her research on the role of the Period genes Per1, Per2, and Per3. These genes, together with the Cry, Clock, and Bmal1 genes, form the central mechanism of the circadian clock by participating in a complex series of negative and positive feedback loops that control their expression levels in a daily rhythm. Genetic studies have linked changes in Period genes, and the Period (PER) proteins that they encode, to the developmental pathways of cancer. Mice with mutations in the Per2 gene develop tumors that are resistant to radiation-induced apoptosis. Wood hypothesized that Per2 mutations might act synergistically to accelerate tumor formation in mice that also had a mutation in the Apc gene, which creates a genetic predisposition for the development of intestinal tumors. They found that mice carrying mutations in both genes did in fact develop almost twice as many tumors as mice carrying the Apc mutation alone.

They investigated the mechanism of this synergistic effect, focusing on two reciprocal hypotheses. One hypothesis is that Per2 affects beta-catenin signaling, which is known to be increased in mice with Apc mutations and is part of the mechanism of tumor formation. The other hypothesis is that Apc mutations might cause abnormalities in circadian clock function, thus affecting Per2 function. Further experiments have provided support for both hypotheses. When unmutated, Per2 was found to suppress the formation of intestinal tumors in mice through a mechanism that involves the regulation of beta-catenin and its downstream targets. On the reciprocal side, they found that both the daily levels and the rhythm of PER2 protein expression were depressed in mice with Apc mutations. These results contribute to a large, developing body of research that suggests that PER proteins act as tumor suppressors, and that reinforces their value as potential targets for anticancer therapies.

Xiaoming Yang, who works with Wood at the University of South Carolina, presented his work, which is intended to further elucidate the role of the Period genes and their encoded proteins in tumors and in normal tissues. Yang described evidence that PER proteins are tumor suppressors, including the observation that overexpression of PER1 or PER2 can inhibit breast cancer growth, as well as the fact that Per mutations, low PER protein expression, and alterations in the epigenetic regulation of Per genes are found in many types of cancers.

PER protein expression is lower in the tumors, with a peak that is 5-fold lower than expression in the liver. The time of peak expression is shifted compared to that in the liver.

Yang found that PER1 and PER2 were expressed with a circadian rhythm in normal mouse liver. Expression of these proteins was high at night and low in the daytime. He found that tumor growth in mice followed a circadian rhythm as well, with peaks in growth rate occurring once at night and once during the day. PER protein expression was lower in the tumors, and the time of peak expression was shifted compared to normal tissues. Yang found alterations in the expression other clock-controlled genes in the tumor as well. Reducing the expression of Per genes in the tumors both increased their growth and altered the circadian growth rhythm. Yang's findings suggest that tumors have their own internal clocks, but that they can respond to signals from the organism's clock as well. The details of these complex interactions remain to be determined. Yang's results also suggest that it is important to take circadian rhythm into account when measuring tumor growth rates, since they change at different times in the daily cycle.

Hematologic malignancies are among the cancers that have been shown to have reduced PER1 and PER2 expression. H. Phillip Koeffler and his group at the University of California, Los Angeles, are studying the role of abnormalities in Per2 gene expression in such malignancies. They are particularly interested in the C/EBP family of transcription factors, which play important roles in energy metabolism, adipogenesis, and myelopoiesis, and have been implicated in the control of Per gene expression as well.

Using cultured cells, Koeffler and his group have shown that two members of this family, C/EBP-α and C/EBP-ε, directly regulate the Per2 promoter. Increased expression of these transcription factors upregulates Per2 expression in human leukemia cell lines. They are investigating the expression of these transcription factors and Per2 in tissue samples from patients with a variety of leukemias and lymphomas. Lymph node and bone marrow samples from acute myeloid leukemia patients show that many have reduced Per2 expression. Patients with diffuse large B-cell lymphomas show reduced Per2 expression as well as dysregulation of C/EBP-α levels. However, these types of changes were not seen in patients with follicular non-Hodgkins lymphoma or mantle cell leukemia. These findings suggest a role for circadian clock genes in the initiation and/or progression of some, but not all, types of leukemia and lymphoma.

William Hrushesky of the University of South Carolina assessed what is known and what needs to be discovered in order to manipulate the circadian clock to control or prevent cancer. He said that in humans it is clear that circadian disruptions alter the host/cancer balance and promote cancer growth. This conclusion can be drawn from many lines of evidence, including epidemiologic research on people with circadian disruptions, genetic research on the associations between cancer risk and clock gene polymorphisms, and from the fact that many human tumors contain clock gene mutations. Much information has also been gathered about the potential role of melatonin in cancer suppression, and preceding speakers had provided significant detail on the experimental systems that have been developed to investigate the mechanisms behind these observations.

Unanswered questions about the role of circadian disruption in cancer.

Yet quite a few unanswered questions remain. What are the relative contributions of the host's versus the tumor's clock in cancer growth? Can clock gene mutations be used as prognostic indicators in human cancers? Melatonin and many clock proteins also have non-clock functions; what is the importance of these functions in cancer initiation and progression? What is the role of host and tumor melatonin receptors in these processes?

Hrushesky noted that cancer might be caused by general circadian disruption, or by the presence of specific clock gene changes that promote abnormal cell growth and proliferation. In the first case, diminishing the disruption and restoring a normal rhythm might be sufficient to prevent or control cancer. This could be done using behavioral, endocrinologic, or pharmacologic interventions. In the second case, however, cancer therapies will need to be targeted at specific genes or gene products to successfully prevent or treat cancer via circadian mechanisms.