TITLE: Induced abortion and breast cancer risk.

AUTHORS: Lazovich D; Thompson JA; Mink PJ; Sellers TA; Anderson KE

AUTHOR AFFILIATION: Division of Epidemiology, School of Public Health, University of Minnesota, Minneapolis 55454-1015, USA.

SOURCE: Epidemiology 2000 Jan;11(1):76-80

CITATION IDS: PMID: 10615848 UI: 20081594

NOTE FROM THE COALITION: This is also a very small study. The low statistical power of the study makes it impossible to determine significance. Lazovich reported an increased risk of breast cancer of 10% for postmenopausal women with histories of having had induced abortions. This study is the fourteenth American study, and the thirteenth to report an increased risk. It is the twenty-seventh of thirty-four worldwide studies to link abortion with breast cancer.

ABSTRACT: Results from case-control studies suggest that induced abortion may be associated with a small increase in risk of breast cancer. While risk estimates from cohort studies have generally not observed such an association, these studies have had limited information regarding abortion and possible confounding variables. Therefore, we conducted a study among a cohort of post-menopausal women from whom detailed information regarding pregnancy outcomes as well as risk factors for breast cancer had been collected. The study sample included 37,247 Iowa Women's Health Study participants, 55-64 years of age at baseline in 1986, who reported no history of breast, or other, cancer (except non-melanoma skin cancer), and for whom information regarding pregnancy outcomes (that is, live birth, stillbirth, spontaneous abortion, ectopic pregnancy or induced abortion) was available. We used linkage with records of the State Health Registry of Iowa, part of the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) program, to estimate the incidence of breast cancer among cohort members through 1995. We calculated age-adjusted relative risks and 95% confidence intervals using Cox proportional hazards regression. Only 653 women (1.8%) reported an induced abortion. The age-adjusted relative risk of breast cancer among women with prior induced abortion compared with those without was 1.1 (95% CI = 0.8-1.6). Relative risks were higher among women whose age at first abortion was less than 20 or at least 30 years, for those whose abortion took place after their first birth or who never gave birth, and for those with early termination (0-2 months). These estimates varied from 1.3-1.7, but the confidence intervals around each were wide. Since most women in this cohort were beyond their reproductive years when abortion became legal in 1973, the low prevalence of induced abortion argues for a cautious interpretation.