Chelbowski Bio Image

Rowan Chlebowski, M.D., Ph.D.

  • Research Professor, Department of Medical Oncology & Therapeutics Research

Rowan Chlebowski, M.D., Ph.D.

Research Focus :
  • Breast cancer
Rowan Chlebowski, M.D., Ph.D., is one of the most influential breast cancer researchers in the world. As a clinical breast oncologist with a Ph.D. in reproductive biology, he has a credentialed clinical and research interest in breast cancer therapy and prevention, menopausal hormone therapy influences on cancer and chronic disease, and lifestyle influences on breast cancer incidence and outcome. He is best known for studying breast cancer issues in the Women's Health Initiative (WHI). He has published widely and led reports in well-cited journals such as JAMA, New England Journal of Medicine, Lancet, Lancet Oncology, Journal of Clinical Oncology, Journal of the National Cancer Institute and JAMA Oncology.
Dr. Chlebowski has received accolades and awards from the American Society of Clinical Oncology, the American Association for Cancer Research and other distinguished societies. He was one of 13 named WHI investigators awarded the "2016 AACR Team Science Award" for groundbreaking work in the women's health area. Based on his body of publications, Dr. Chlebowski has been on the Thomson Reuters "Most Influential Scientific Minds" for the last two years, which is based on the highest number of highly cited papers over the most recent decade, defined as the top 1 percent most cited in the area of clinical medicine. He is one of only 14 breast oncologists on the worldwide list.
  • 2017 – present, Research Professor, Department of Medical Oncology & Therapeutics Research, City of Hope, Duarte, CA
  • 2004 – 2017, Senior Investigator, Los Angeles Biomedical Research Institute at Harbor-UCLA, Los Angeles, CA
  • 1999 – 2017, Chief, Division of Medical Oncology and Hematology, Harbor-UCLA Medical Center, Los Angeles, CA
  • 1990 – 2017, Professor of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA
  • 1979 – 1990, Assistant/Associate Professor of Medicine, UCLA, Harbor UCLA Medical Center, Los Angeles, CA
  • 1976 – 1979, Los Angeles County + USC Medical Center, Medical Oncology Fellowship, Clinical Instructor, Los Angeles, CA
  • 1974 – 1976, Cleveland Metropolitan General Hospital (Metro Health), Residency in Internal Medicine, Cleveland, OH
  • Medical Oncology & Therapeutics Research


  • 1969 - 1974, Case Western Reserve University, School of Medicine, M.D., Ph.D., Reproductive Biology
  • 1968 - 1969, University of Wisconsin, Developmental Biology
  • 1963 - 1968, Marquette University, B.S., Magna Cum Laude
Dr. Chlebowski has led full-scale, multicenter randomized trial reports from studies in the Women's Health Initiative (WHI) evaluating estrogen plus progestin, estrogen alone, calcium and vitamin D, and dietary modification influence on breast cancer incidence and outcome. The WHI JAMA report he led showing that estrogen plus progestin increased breast cancer incidence, delayed breast cancer diagnosis, and increased deaths from breast cancer led to a change in menopausal hormone therapy use around the world.
In two New England Journal of Medicine (NEJM) publications, he helped identify a subsequent drop in breast cancer incidence in the U.S. and subsequently reported findings from the WHI randomized trial which supported the hypothesis linking the drop in estrogen plus progestin use with the drop in breast cancer incidence. Follow-up for the landmark WHI clinical trials continues as Dr. Chlebowski recently updated results from the WHI Dietary Modification trial where a statistically significant reduction in deaths after breast cancer was seen in the dietary intervention group after over 16 years median follow-up.
In a parallel study, Dr. Chlebowski led the report from the Women's Intervention Nutrition Study (WINS), a full scale adjuvant breast cancer trial, presented at an American Society of Clinical Oncology (ASCO) Plenary Session and published in Journal of the National Cancer Institute, which demonstrated for the first time that a lifestyle intervention, namely dietary fat intake reduction, could affect a cancer outcome. This finding was hailed in a subsequent New York Times editorial.
Dr. Chlebowski's involvement in a broad scope of research projects has led to substantial and ongoing involvement in ASCO guideline development. He led the initial ASCO Technology Assessment reviewing the initial tamoxifen breast cancer prevention trials which led to an invited review on breast cancer chemoprevention in NEJM. Dr. Chlebowski's role on the ASCO breast cancer prevention guideline has been ongoing. He also participated in the ASCO guideline evaluating aromatase inhibitors in early breast cancer and in the ASCO guideline for bisphosphonate and bone health considerations in breast cancer management. In a related clinical trial, Dr. Chlebowski was an author on the NEJM MAP.3 primary prevention trial where the aromatase inhibitor exemestane was associated with a 65 percent reduction in breast cancer incidence.
Chlebowski RT, Aragaki AK, Thomson CA, Anderson GL, Manson JE, Simon MS, Rohan TE, Snetselaar L, Barrington W, Vitolins M, Womack C, Qi L, Hou L, Thomas F, Prentice RL. Low-fat dietary pattern and breast cancer mortality in the Women’s Health Initiative (WHI) randomized controlled trial.  J Clin Oncol 2017 Jun 27:JCO2016720326. DOI: 10.1200/JCO.2016.72.0326. [Epub ahead of print]

Earlier Women’s Health Initiative Dietary Modification trial findings suggested that a low-fat eating pattern may reduce breast cancers with greater mortality. Therefore, we examined the long-term influence of this intervention on deaths as a result of and after breast cancer during 8.5 years (median) of dietary intervention and cumulatively during 16.1 years (median) of follow-up.

Patients and Methods
The trial randomly assigned 48,835 postmenopausal women with normal mammograms from 1993 to 1998 at 40 US clinical centers to a dietary intervention with goals of a reduction of fat intake to 20% of energy and an increased intake of fruits, vegetables, and grains (40%; n=19,541) or to a usual diet comparison (60%; n=29,294).

In the dietary group, fat intake and body weight decreased (all P<0.001). During the 8.5 year dietary intervention, fewer deaths occurred as a result of breast cancer in the dietary group, which was not statistically significant (hazard ratio [HR], 0.67; 95% CI, 0.43 to 1.06; P=0.08). During the same period, deaths after breast cancer were significantly reduced (HR 0.65; 95% CI, 0.45-0.94; P=0.02) by the dietary intervention. During the 16.1 year follow-up, with deaths after breast cancer also were significantly reduced (HR 0.82; 95% CI, 0.70 to 0.96; P=0.01) in the dietary group.

Compared with a usual diet comparison group, a low-fat dietary pattern led to a lower incidence of deaths after breast cancer.

Chlebowski RT, Anderson GL, Gass M, Lane DS, Aragaki AK, Kuller LH, Manson JE, Stefanick ML, Ockene J, Sarto GE, Ravdin PM, Schenken R, Hendrix SL, Rajkovic A, Rohan TE, Yasmeen S, Prentice RL. Influence of estrogen plus progestin on breast cancer incidence and mortality. JAMA 2010; 304(15):1684-1692.

CONTEXT: in the Women’s Health Initiative randomized, placebo-controlled trial of estrogen plus progestin, after a mean intervention time of 5.6 (SD, 1.3) years (range, 3.7-8.6 years) and a mean follow-up of 7.9 (SD, 1.4) years, breast cancer incidence was increased among women who received combined hormone therapy.

OBJECTIVE: To determine the effects of therapy with estrogen plus progestin on cumulative breast cancer incidence and mortality.

DESIGN, SETTING, AND PARTICIPANTS: A total of 16,608 postmenopausal women aged 50 to 79 years with no prior hysterectomy from 40 US clinical centers were randomly assigned to receive combined conjugated equine estrogens, 0.625 mg/d, plus medroxyprogesterone acetate, 2.5 mg/d, or placebo pill.

MAIN OUTCOME MEASURES: Invasive breast cancer incidence and breast cancer mortality.

RESULTS: In intention-to-treat analyses, estrogen plus progestin was associated with more invasive breast cancers compared with placebo. There were more deaths directly attributed to breast cancer (HR 1.96; 95% CI, 1.00-4.04; P=0.049) as well as more deaths from all causes occurring after a breast cancer diagnosis (HR 1.57; 95% CI, 1.01-2.48; P=0.045) among women who received estrogen plus progestin compared with women in the placebo group.

CONCLUSIONS: Estrogen plus progestin was associated with greater breast cancer incidence. Breast cancer mortality also appears to be increased with combined use of estrogen plus progestin.
Chlebowski RT, Kuller L, Prentice RL, Stefanick M, Manson J, Gass M, Aragaki A, Ockene J, Lane D, Sarto G, Schenken R, Hendrix S, Ravdin P, Rohan T, Yasmeen S, Anderson G. Breast cancer after estrogen plus progestin use in postmenopausal women. N Engl J Med 2009; 360(6):573-587.

Following the release of the 2002 report of the Women’s Health Initiative (WHI) trial of estrogen plus progestin, the use of menopausal hormone therapy in the United States decreased substantially. Subsequently, the incidence of breast cancer also dropped, suggesting a cause-and-effect relation between hormone treatment and breast cancer. However, the cause of this decrease remains controversial.

We analyzed the results of the WHI randomized clinical trial – in which one study group received 0.625 mg of conjugated equine estrogens plus 2.5 mg of medroxyprogesterone acetate daily and another group received placebo – and examined temporal trends in breast cancer diagnoses.

In the clinical trial, an increase in breast cancer diagnoses was seen in the group receiving estrogen plus progestin over the course of the 5.6 year intervention period. The elevated risk decreased rapidly after both groups stopped taking the study pills, despite a similar frequency of mammography.

The increased risk of breast cancer associated with the use of estrogen plus progestin declined markedly soon after discontinuation of combined hormone therapy and was unrelated to changes in frequency of mammography.

Chlebowski RT, Blackburn G, Thomson CA, Nixon DW, Shapiro A, Hoy MK, Goodman MT, Giuliano AE, Karanja N, McAndrew P, Hudis C, Butler J, Merkel D, Kristal A, Caan B, Michaelson R, Vinciguerra V, Del Prete S, Winkler M, Hall R, Simon M, Winters BL, Elashoff RM. Dietary fat reduction and breast cancer outcome: Interim efficacy results from the Women’s Intervention Nutrition Study (WINS) J Natl Cancer Inst 98(24):1767-76, 2006.

BACKGROUND: Preclinical and observational studies suggest a relationship between dietary fat intake and breast cancer, but the association remains controversial. We carried out a randomized, prospective, multicenter clinical trial to test the effect of a dietary intervention designed to reduce fat intake in women with resected, early-stage breast cancer receiving conventional cancer management.

METHODS: A total of 2,437 women were randomly assigned dietary intervention (n=975) or control (n=1462). Relapse-free survival was examined using Kaplan-Meier analysis, stratified log-rank tests, and Cox proportional hazards models. Statistical tests were two-sided.

RESULTS: Dietary fat intake was lower in the intervention than in the control group (fat grams/day at 12 months, P<0.001) (corresponding to a statistically significant P=0.005), 6 pounds lower mean body weight in the intervention group. The hazard ratio of relapse events in the intervention group compared with the control group was 0.76 (95% CI, 0.60-0.98, P=0.77 for stratified log rank and P=0.034 for adjusted Cox model analysis). Exploratory analyses suggested a differential effect of the dietary intervention based on hormonal receptor status.

CONCLUSIONS: A lifestyle intervention reducing dietary fat intake, with modest influence on body weight, may improve relapse-free survival of breast cancer patients receiving conventional cancer management.
  • American Society of Clinical Oncology
  • American Association for Cancer Research
  • American Society of Preventive Oncology
  • 2008, Fellow of the American Society of Clinical Oncology (FASCO)
  • 2012, ASCO-American Cancer Society Award and Lecture, 2012 recipient. This special award is presented at the ASCO Annual Meeting to recognize a person who has made a significant contribution to cancer prevention and control, research or practice.
  • 2012, Case Western Reserve University School of Medicine Distinguished Alumni Award
  • 2013, ESMO Annual Meeting Presidential Session: Best and Late Breaking Abstracts
  • 2014, NAMS Lippincott/Williams & Wilkins Menopause Journal Best Paper of the Year Award
  • 2014, Thomson Reuters the World’s Most Influential Scientific Minds 2014 and 2015 List (Based on the greatest number of highly cited papers – ranking among the top 1 percent most cited on topic between 2003 and 2014. A total of 14 breast cancer oncologists on worldwide list.)
  • 2015, People for Others Award from the Klingler College of Arts and Sciences, Marquette University, joint award with spouse Joan Chlebowski, M.D.
  • 2016, American Association for Cancer Research 2016 Team Science Award to the Women’s Health Initiative (WHI) Investigators. Dr. Chlebowski is one of 13 named WHI investigator group members.The award recognizes an outstanding interdisciplinary research team for innovative and meritorious science with cancer impact.
  • 2016 , Web of Science Highly Cited Researcher 2016
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