J. Am. Physicians & Surgeons: Induced Abortion and Breast Cancer Risk: A Critical Analysis of the Report of the Harvard Nurses Study II.

• Author: Brind, Joel
• Position: Reprint

Harvard researchers have reported the widely disseminated conclusion: "Among this predominantly premenopausal population, neither induced nor spontaneous abortion was associated with the incidence of breast cancer." This conclusion was based on the results of ten years of followup of participants in the Harvard Nurses Study II, between 1993 and 2003. Data were gathered from baseline questionnaires returned by more than 105,000 women in 1993, and every two years thereafter by women who were 39-56 years of age in 2003. This conclusion appears to be straightforward and unambiguous, however, several serious methodological errors cast doubt on the validity of its overall result.

One error in prospective studies is the relatively short period of followup, in contrast to most retrospective case-control studies. Since the induction of breast cancer by an exposure such as induced abortion typically takes eight to ten years, the inclusion of women with very recent abortions will artificially lower the observed association. The proper exclusion of women with recent abortions would not have substantially decreased the statistical power of the study, yet it would have eliminated an obvious...