Women with a strong family history of breast cancer who had taken older oral contraceptives may have an increased risk of developing breast cancer, a new study indicates. Oral contraceptives containing the hormones estrogen and progestin have been on the market for over 35 years. Those formulated before 1975 were more likely to have higher doses of both, but since 1975 they have had lower doses to reduce side effects and the risk of vascular disease. The relationship between oral contraceptives and breast cancer is less clear. In studies of the general population, the pill has been associated with a slightly increased risk of breast cancer up to 10 years after a woman stops using them.
Researchers are uncertain of the impact in women with a family history of breast cancer.
Dawn M. Grabrick, M.P.H., of Mayo Clinic, Rochester, Minn., and colleagues at Mayo and the University of Minnesota studied more than 400 families of women diagnosed with breast cancer between 1944 and 1952. From 1991 to 1996 the team interviewed relatives about their history of cancer and risk factors for breast cancer. Among women whose mothers or sisters had breast cancer, those who had ever taken oral contraceptives formulated before 1975 had a 3.3 times higher risk of developing breast cancer than those who had never taken oral contraceptives. The risk was even higher in families in which five or more blood relatives had breast or ovarian cancer. Women whose mothers or sisters had breast cancer and who ever took the pill, whether formulated before or after 1975, were 11.4 times more likely to develop the disease than those who had not taken it.