Professor and Director
Department of Cancer Etiology
Division of Population Science
Dean for Faculty Development
City of Hope National Medical Center
An award-winning pioneer in breast cancer research, Leslie Bernstein led the first major studies suggesting that exercise might help women lower their risk for the disease via its impact on hormonal activity. She continues that groundbreaking research today, all the while mentoring a new generation of gifted investigators.
Leslie's career as a scientist took flight despite a rather late start. She was recruited into a fledgling program in biostatistics in 1958 after her sophomore year at UCLA but a number of life events intervened before she completed her BA in mathematics there. She eventually entered graduate school at the University of Southern California (USC) in biostatistics in her late 30s and obtained her PhD.
Leslie then spent the next 25 years as faculty in USC’s Department of Preventive Medicine where she held the AFLAC, Inc., Chair in Cancer Research; this past year she moved to the Beckman Research Institute/City of Hope National Medical Center.
Over the years, Leslie has forged a successful career as a biostatistician and epidemiologist with a primary research emphasis on breast cancer etiology and prevention. Her research has shown how endogenous and exogenous hormones, physical activity, and obesity influence breast cancer risk; how personal and lifestyle risk factors interact with breast cancer treatment to affect the subsequent risk of other chronic diseases; and how physical activity affects breast cancer prognosis and influences the breast cancer survivor’s quality of life.
Leslie has also conducted research studies identifying risk factors for esophageal cancers and non-Hodgkin’s lymphomas. For 20 years Leslie served as the scientific director for the Los Angeles County Cancer Surveillance Program, a member of the Surveillance, Epidemiology and End Results (SEER) registry system and part of California’s statewide cancer registry system, where she developed innovative studies using registry data.
However, it is through her work on breast cancer risk factors and prevention that Leslie has earned the most acclaim. This past year, she received the American Association for Cancer Research (AACR) Cancer Research and Prevention Foundation Award for Excellence in Cancer Prevention Research, as well as the Brinker Award for Scientific Distinction in the Field of Clinical Science from the Susan G. Komen for the Cure Foundation. These awards cited her research challenging the paradigm that epidemiologic risk factors for breast cancer were largely unmodifiable and noted that her research on physical activity and breast cancer provided the evidence base for one of the few lifestyle recommendations that can be made for breast cancer risk-reduction.
Her interest in breast cancer was spurred by her early work evaluating circulating hormone levels in women at high and low risk of breast cancer and in breast cancer cases and controls. These studies demonstrated that pregnancy permanently lowers levels of prolactin and estradiol among premenopausal women; that women in Asia have lower estrogen levels than US white women, premenopausally and postmenopausally; and that women with breast cancer have higher circulating estrogen levels than healthy control women.
In the 1980s, understanding of breast cancer risk factors focused on the hormonal implications and the hormone responsiveness of breast tissue. But as a new investigator, Leslie began to think beyond the established risk factors - race/ethnicity, age, family history, age at menarche, age at menopause, timing of pregnancies and pregnancy outcomes. If ovarian hormones and menstrual cycle patterns were critically important, she felt that factors or behaviors that altered menstrual cycle patterns could be identified that would also impact breast cancer risk.
She and her colleagues proposed that physical activity was such a factor because it altered menstrual cycle patterns in a sequence that progressed from minor alterations in cycle phases with light activity to more substantial changes among elite athletes who experienced the cessation of menses during training. Leslie designed studies to address three questions: does physical activity influence a girl’s age at menarche; does moderate activity during adolescence influence the frequency of ovulatory menstrual cycles; and does physical activity affect the risk of breast cancer? Her studies of school girls and women have documented that the answer to each of these questions is, "Yes."
She conducted the first case-control study designed to assess directly the influence of exercise activity on breast cancer risk, collecting lifetime histories of recreational activity using a calendar of life-events approach. Her study of women ages 40 years and younger clearly demonstrated that activity during adolescence lowered breast cancer risk and that average lifetime activity was the strongest predictor of risk. She followed this study with a series of case-control studies of postmenopausal women, Asian American women, and African American women showing again a marked impact of lifetime physical activity on breast cancer risk.
The goal of these research projects was to lay the foundation for understanding how a lifestyle factor - recreational physical activity - would alter hormonal processes, and thereby result in a lower risk of breast cancer. Her work also assessed whether these effects were modified by age at activity, attained age, pregnancy history, family history of breast cancer or body mass index. Leslie has continued to work on issues related to breast cancer throughout her career.
Over the past 13 years, Leslie has been involved first in developing and, now, in conducting the California Teachers Study, a cohort of more than 133,000 women who are public school professionals in California. As principal investigator for this study, she coordinates researchers at 5 California institutions who collaborate on the study. The California Teachers Study has provided a number of important findings including that long-term physical activity reduces breast cancer risk, and that the benefit is most apparent for ER-negative invasive breast cancers and in situ disease.
In addition to her research activities, Leslie served for 8 years as Senior Associate Dean for Faculty Affairs at the USC Keck School of Medicine, and for 2 years as USC’s Vice Provost for Medical Affairs. At the USC/Norris Comprehensive Cancer Center she was co-leader for the Women’s Cancers Program. At the City of Hope, she directs the Department of Cancer Etiology and serves as the institution-wide Dean of Faculty. She chairs a number of important committees for her colleagues including advisory committees for the Harvard Nurses Health Study, the Sisters Study at the National Institute for Environmental Health Sciences and the MD Anderson Cancer Center Texas Mexican-American Cohort Study. She recently completed 5 years’ service as a member of NCI’s Board of Scientific Counselors and serves on NCI’s Program Project Grant review committee (Committee E). She has served on the editorial boards for Cancer Epidemiology, Biomarkers and Prevention and Epidemiology and is currently on the editorial board for Obesity.
Throughout her career, Leslie has taken seriously her role as a mentor. This was clearly exemplified when she served as the chief mentor for USC’s medical school in her dean’s role. After this, she initiated a mentoring program for PhD students and postdoctoral fellows in the Department of Preventive Medicine and chaired the Department’s Appointments, Promotions and Tenure Committee, helping faculty to prepare for promotion and developing a mentoring plan to support their careers. She has personally mentored more than 100 students, postdocs, and junior faculty, who have subsequently gone on to productive careers in cancer research. She continues to chair PhD student committees for USC students retaining the title of professor emerita at USC, and is now developing mentoring programs at the City of Hope. Further, she has earned a national reputation as a strong advocate and mentor for women in her field.
Leslie received a BA with highest honors in mathematics from UCLA, a masters degree in gerontology from USC, and a PhD in biostatistics from USC. She and her husband, Saul, a pediatric orthopedic surgeon, have 3 adult children and 11 "incredible" grandchildren. Many evenings, she consults with her 4 granddaughters, ages 15 and 16, to explain concepts they are learning in their advanced algebra and precalculus classes.