August 1, 2014

Recently using some birth control pills may raise breast cancer risk

But link not found with other, lower-dose estrogen pills

Seattle, WA—Women who recently used birth control pills containing high-dose estrogen and a few other formulations had an increased risk for breast cancer, whereas women using some other formulations did not, according to a report about Group Health patients published in Cancer Research, a journal of the American Association for Cancer Research.

“Our results suggest that use of contemporary oral contraceptives [birth control pills] in the past year is associated with an increased breast cancer risk relative to never or former oral contraceptive use, and that this risk may vary by oral contraceptive formulation,” said Elisabeth F. Beaber, PhD, MPH, a staff scientist in the Public Health Sciences Division of Fred Hutchinson Cancer Research Center in Seattle, Washington. She also has a joint affiliation at Group Health Research Institute.

“Our results require confirmation and should be interpreted cautiously,” Beaber added. “Breast cancer is rare among young women and there are numerous established health benefits associated with oral contraceptive use that must be considered. In addition, prior studies suggest that the increased risk associated with recent oral contraceptive use declines after stopping oral contraceptives.”

In a nested case-control study of 1,102 women diagnosed with breast cancer and 21,952 controls, Beaber and colleagues found that recent oral contraceptive use increased breast cancer risk by 50 percent, compared with never or former use. All study participants were at Group Health Cooperative in the Seattle-Puget Sound area. Patients received a cancer diagnosis between 1990 and 2009.

Birth control pills containing high-dose estrogen increased breast cancer risk 2.7-fold, and those containing moderate-dose estrogen increased the risk 1.6-fold. Pills containing ethynodiol diacetate increased the risk 2.6-fold, and triphasic combination pills containing an average of 0.75 milligrams of norethindrone increased the risk 3.1-fold.

Birth control pills containing low-dose estrogen did not increase breast cancer risk.

About 24 percent, 78 percent, and less than 1 percent of study controls who were recent oral contraceptive users filled at least one prescription in the past year for low-, moderate-, and/or high-estrogen dose oral contraceptives, respectively, according to Beaber.

Unlike most previous studies that depended on women’s self-report or recall, which may cause bias, Beaber and colleagues used electronic pharmacy records to gather detailed information on oral contraceptive use including drug name, dosage, and duration of medication.

This study was funded by the National Cancer Institute.

Dr. Beaber’s co-authors were Diana S.M. Buist, PhD, MPH, a senior investigator at Group Health Research Institute; William E. Barlow, PhD, of Cancer Research & Biostatistics (CRAB), Kathleen E. Malone, PhD, and Christopher I. Li, MD, PhD, of the Fred Hutch; and Susan D. Reed, MD, MPH, an associate professor at the University of Washington (UW) School of Medicine and an affiliate investigator at Group Health Research Institute. Drs. Buist, Barlow, Malone, Li, and Reed are also affiliated with the UW School of Public Health.

American Association for Cancer Research

Founded in 1907, the American Association for Cancer Research (AACR) is the world’s oldest and largest professional organization dedicated to advancing cancer research and its mission to prevent and cure cancer. AACR membership includes more than 34,000 laboratory, translational, and clinical researchers; population scientists; other health care professionals; and cancer advocates residing in more than 90 countries. The AACR marshals the full spectrum of expertise of the cancer community to accelerate progress in the prevention, biology, diagnosis, and treatment of cancer by annually convening more than 20 conferences and educational workshops, the largest of which is the AACR Annual Meeting with more than 18,000 attendees. In addition, the AACR publishes eight peer-reviewed scientific journals and a magazine for cancer survivors, patients, and their caregivers. The AACR funds meritorious research directly as well as in cooperation with numerous cancer organizations. As the Scientific Partner of Stand Up To Cancer, the AACR provides expert peer review, grants administration, and scientific oversight of team science and individual grants in cancer research that have the potential for near-term patient benefit. The AACR actively communicates with legislators and policymakers about the value of cancer research and related biomedical science in saving lives from cancer. Follow the AACR on Twitter: @AACR. Follow the AACR on Facebook: http://www.facebook.com/aacr.org.

Fred Hutchinson Cancer Research Center

At Fred Hutchinson Cancer Research Center, home to three Nobel laureates, interdisciplinary teams of world-renowned scientists seek new and innovative ways to prevent, diagnose, and treat cancer, HIV/AIDS and other life-threatening diseases. Fred Hutch’s pioneering work in bone marrow transplantation led to the development of immunotherapy, which harnesses the power of the immune system to treat cancer with minimal side effects. An independent, nonprofit research institute based in Seattle, Fred Hutch houses the nation’s first and largest cancer prevention research program, as well as the clinical coordinating center of the Women’s Health Initiative and the international headquarters of the HIV Vaccine Trials Network. Private contributions are essential for enabling Fred Hutch scientists to explore novel research opportunities that lead to important medical breakthroughs. Follow Fred Hutch on Facebook, Twitter, or YouTube.

About Kaiser Permanente Washington Health Research Institute

Kaiser Permanente Washington Health Research Institute (KPWHRI), formerly Group Health Research Institute, improves the health and health care of Kaiser Permanente members and the public. The Institute has conducted nonproprietary public-interest research on preventing, diagnosing, and treating major health problems since 1983. Government and private research grants provide our main funding. Follow KPWHRI research on Twitter, Facebook, Pinterest, LinkedIn, or YouTube. For more information, go to: www.kpwashingtonresearch.org.

About Kaiser Permanente

Kaiser Permanente is committed to helping shape the future of health care. We are recognized as one of America’s leading health care providers and not-for-profit health plans. Founded in 1945, Kaiser Permanente has a mission to provide high-quality, affordable health care services and to improve the health of our members and the communities we serve. We currently serve more than 12.2 million members in eight states and the District of Columbia. Care for members and patients is focused on their total health and guided by their personal Permanente Medical Group physicians, specialists and team of caregivers. Our expert and caring medical teams are empowered and supported by industry-leading technology advances and tools for health promotion, disease prevention, state-of-the-art care delivery and world-class chronic disease management. Kaiser Permanente is dedicated to care innovations, clinical research, health education and the support of community health. For more information, go to: kp.org/share.


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