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so that researchers could present new and unpublished findings.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.