BETHESDA, MarylandWell-established epidemiological evidence shows that neither an induced nor a recognized spontaneous abortion increases a woman’s risk of breast cancer, a workshop convened by the National Cancer Institute (NCI) concluded after an extensive review of the available scientific data. However, important gaps exist in the understanding of how events prior to and during pregnancy may affect a woman’s risk of malignant breast tumors, and those gaps need to be filled, the workshop’s report added (see Table).
The "Early Reproductive Events and Breast Cancer Workshop" attracted some 120 scientists to assess the state of the evidence regarding breast cancer risk factors associated with pregnancy. At one point, the public meeting was closed so that researchers could present new and unpublished findings.
Epidemiologist Leslie Bernstein, PhD, of the University of Southern California’s Keck School of Medicine, presented the workshop’s findings and recommendations to a joint meeting of NCI’s Board of Scientific Counselors and Board of Scientific Advisors. After hearing her report, the two boards voted unanimously to accept the workshop report.
Federal law requires that an NCI advisory board accept such a report before it can be forwarded to the institute’s director for consideration and action.
The issue of whether induced abortions increase breast cancer riskwhich in part stimulated NCI director Andrew C. von Eschenbach, MD, to convene the workshopdrew considerable public attention to the meeting. A few studies have indicated a possible link. However, the workshop rated the evidence "well established" that an abortion, whether induced or spontaneous and recognized by the woman, does not increase the risk of breast cancer. The researchers could not address the issue of all spontaneous abortions because "a large portion of spontaneous abortions are not recognized by women, and it is difficult to record those," Dr. Bernstein said.
Other Epidemiological Findings
Six other epidemiological findings received well-established ratings: (1) Early age at first term birth is related to a lifetime decrease in breast cancer risk; (2) increasing parity is associated with a long-term risk reduction, even when controlling for age at first birth; (3) the additional long-term protective effect of young age at subsequent term pregnancies is not as strong as for the first term pregnancy; (4) a nulliparous woman has approximately the same breast cancer risk as a woman with a first term birth around age 30; (5) breast cancer risk is transiently increased after a term pregnancy; and (6) long-duration lactation provides a small additional risk reduction after consideration of age at, and number of, term pregnancies.