TITLE: Abortion history and breast cancer risk: results from the Shanghai breast cancer study.

Amer J Epidemiology, June 1, 2000;151 (11)

M Sanderson, XO Shu, F Jin, Q Dai, WQ Wen, Y Hui, YT Gao, W Zheng (university of South Carolina, SC, 29208)

Studies of the association between induced abortion and breast cancer risk have been inconsistent, perhaps due to suspected underreporting of abortions. Induced abortion is a well-accepted family control procedure in China, and women who have several induced abortions do not feel stigmatized. The authors used data from a population case-control study of breast cancer among women age 25 to 64 conducted between 1996 and 1998 in urban Shanghai to assess whether a history and number of induced abortions was related to breast cancer risk. In-person interviews were completed with 1459 incident breast cancer cases ascertained through a population-based cancer registry, and 1556 controls randomly selected from the general population in Shanghai (with respective response rates of 91% and 90%). After adjusting for confounding, there was no relation between ever having had an induced abortion and breast cancer (odds ratio [OR] 1.0; 95% confidence interval [CI] 0.8-1.2). While women who had 3 or more induced abortions were not at increased risk of premenopausal breast cancer (OR 0.9; 95% CI 0.6-1.3) there was an elevated risk of postmenopausal breast cancer (OR 1.6, 95% CI 0.9-2.8). Among women whose first birth was at age 26 or older, the effect of having 3 or more abortions differed by menopausal status (premenopausal : OR 0.4, 95% CI 0.2-0.8; postmenopausal: OR 1.7, 95% CI 0.9-3.3). These results suggest that a history of several induced abortions may influence risk of premenopausal and postmenopausal breast cancer differently.