Modification of oral contraceptive relationships on breast cancer risk by selected factors among younger women.

ABSTRACT

PIP: To assess the possible interactive effects of oral contraceptives (OCs) with selected breast cancer risk factors, a case-control study involving US women diagnosed with breast cancer before 45 years of age was conducted. All incident cases of breast cancer diagnosed among younger women during 1990-92 in Atlanta, Georgia, Seattle/Puget Sound, Washington, and five counties of central New Jersey were eligible. Controls were identified through random-digit dialing. The final sample consisted of 1647 cases and 1501 controls. Ever-use of OCs for 6 months or more was associated with a slightly elevated breast cancer risk (relative risk (RR), 1.3; 95% confidence interval (CI), 1.1-1.5), with a stronger association for women whose breast cancer was diagnosed prior to age 35 years (RR, 1.8; 95% CI, 1.2-2.7). Among women under age 35 years, the risk was highest among women who had used OCs for 5 or more years and for those who used them within the past 5 years. In general, study findings did not support extensive variations in the risk associated with OC use across most risk factors. However, there were some noteworthy variations. At ages 35-44 years, long-term OC use exerted stronger effects in African-American women (RR, 1.5; 95% CI, 0.9-2.6) and other non-White women (RR, 2.8; 95% CI, 1.2-6.6) than among White women (RR, 1.0; 95% CI, 0.8-1.3). Although there was no interaction between OC use and a family history of breast cancer, OC use by a woman with a sister with breast cancer elevated the cancer risk. Body size was inversely associated with breast cancer risk in OC users, while weekly consumption of 7 or more alcoholic drinks slightly raised this risk.