Abstract

PIP: The risk of breast cancer in relation to oral contraceptive (OC) use was evaluated in a case-control study of 1191 breast cancer patients and 5026 controls. Women, 20-59, were interviewed in 1976-81. Particular attention was given to OC use of long duration that began or ended at least 10 years prior to the study, and to categories of women with increased baseline risk. For ever-use compared with never-use, the estimated relative risk (RR) of breast cancer was 1.0 (95% confidence interval (CI) 0.9-1.2). Use of OCs for 5 or more years was not associated with breast cancer, regardless of whether use had ended as much as 10 or more years previously or more recently. The RR estimate was elevated (2.2, CI 0.9-5.6) among women ages 30-39 for use that lasted 5-9 years and began 15 or more years previously. However, the RR for 10 or more years of use beginning 15 or more years before the study period was compatible with unity, suggesting that the former was a chance finding. Within categories of women whose baseline risk was elevated, including nulligravidae, premenopausal women, and those with benign breast disease or history of breast cancer in 1st-degree relatives, the RR estimates for 5 or more years of use approximated 1.0. For any use before 1st pregnancy, the RR was 1.3; for use lasting 3 or more years, it was 0.9. These data suggest that longterm OC use does not increase the risk of breast cancer, even after a latent interval exceeding 1 decade. This study also gives little support to earlier suspicions that OC use increases the risk in special categories of women.