Oral contraceptive use and early abortion as risk factors for breast cancer in young women

Abstract

A case-control study was conducted in Los Angeles County, California, of 163 very young breast-cancer cases (all aged 32 or less at diagnosis) to investigate the role, if any, of oral contraceptives (OC) in the development of the disease. OC use before first full-term pregnancy (FFTP) was associated with an elevated risk, which increased with duration of OC use (relative risk approximately 2.2 at 6 years of use, P < 0.01). This increased risk could not be explained by other risk factors. OC use after FFTP was not associated with any change in risk. A first-trimester abortion before FFTP, whether spontaneous or induced, was associated with a 2.4-fold increase in breast-cancer risk (P < 0.005).

PIP: A case control study was conducted in Los Angeles County, California of 163 breast cancer cases (all aged 32 or less at diagnosis) to determine the role, if any, of oral contraceptives (OCs) in the development of the disease. The patients were white women with microscopically confirmed breast cancer 1st diagnosed between July 1972 and December 1978. The patients were identified by the University of Southern California Cancer Surveillance Program (CSP), the population based cancer registry for Los Angeles County. 2 individually matched controls were sought for each of the 163 study patients. The 1st control was a neighborhood control, and the 2nd a friend control. The relative risk for breast cancer was statistically significantly increased by a history of the disease in mother or sister, by a history of benign breast disease, by earlier menarche, and by longterm use of OCs. The relative risk was decreased by having had a full-term (28 weeks or longer) pregnancy, but the result was not statistically significant. There was no clear trend with the age at 1st full-term pregnancy. Relative risk for OC use was roughly doubled if only use before 1st full-term pregnancy was considered. Relative risk was 3.5 for 8 or more years' use before 1st full-term pregnancy, and the trend of increasing relative risk with increasing duration of use was statistically highly significant. A 1st trimester abortion before 1st full-term pregnancy, whether spontaneous or induced, was associated with a 2.4-fold increase in breast cancer risk.