Abortion, breast cancer not linked, data say
A new analysis of worldwide evidence on the possible relation between breast cancer and previous spontaneous and induced abortions reaffirms earlier findings that pregnancies that end in abortion do not increase a woman’s risk of developing breast cancer.1
The report on the meta-analysis "agrees exactly" with information presented at a March 2003 workshop held by the Bethesda-based National Cancer Institute (NCI), says Leslie Bernstein, PhD, professor of preventive medicine at the Keck School of Medicine, University of Southern California in Los Angeles.2 The report also concurs with a July 2003 committee opinion issued by the Washington, DC-based American College of Obstetricians and Gynecologists, which found no evidence supporting a causal link between induced abortion and subsequent development of breast cancer.3
The federal government had previously suggested that abortion might raise the risk of breast cancer. An NCI fact sheet on the issue was revised in November 2002 to say the evidence for a link between induced abortions and breast cancer was inconclusive. It was changed in May 2003 to reflect the findings of the March 2003 workshop. (To access the fact sheet, "Abortion, Miscarriage, and Breast Cancer Risk Sheet," go to www. cancer.gov and click on "Cancer Information," "Prevention, Genetics, Causes," "Breast Cancer: Prevention, Genetics, Causes," then the publication title.)
Currently, three states — Minnesota, Mississippi, and Texas — have laws in effect that require providers to counsel women on the purported abortion/breast cancer link, according to Chinué Richardson, public policy assistant at the Washington, DC, bureau of the Alan Guttmacher Institute. The information comes in state-directed counseling that is required prior to the abortion procedure. Women must wait 24 hours after receiving the counseling before having an abortion.4
Look at the findings
The new analysis came from an international collaboration of scientists, led by a team of researchers from the University of Oxford in England. The group focused on the "obvious need to consider completely and separately the studies with prospectively recorded information on previous induced abortions," explains Sir Richard Peto, FRS, professor of medical statistics and epidemiology at the University and co-author of the analysis.
The group re-analyzed original information from 53 epidemiological studies from 16 countries, including previously unpublished data. Relative risks of breast cancer (comparing the effects of having had a pregnancy that ended in an abortion with those of never having had that pregnancy) were calculated and stratified by study, age at diagnosis, parity, and age at first birth. Results of studies that used prospective information on abortion (recorded before the diagnosis of breast cancer) were considered separately from results of studies that used retrospective information (recorded after the diagnosis of breast cancer).
In reporting the relative risk (wherein a value of 1.0 or less indicates no adverse effect on the risk of developing breast cancer), the researchers found a 0.98 relative risk for women who have had a spontaneous abortion and a 0.93 relative risk for women who have had an induced abortion. The group plans to look at relevance of age and timings of any full-term pregnancies to breast cancer incidence in its next round of research, states Peto.
Why have some researchers linked abortion to an increased risk for breast cancer? According to the new analysis, studies of breast cancer with retrospective recording of induced abortion may have lead to "misleading results," perhaps because women who had developed breast cancer were, on average, more likely than other women to disclose previous induced abortions.1
Bernstein does not agree with that assessment. She says she believes well-designed case-control studies can yield the same level of data as cohort investigations. The key point for providers to take away from the new analysis is that the evidence showing that induced abortion is not associated with an increase in breast cancer risk is well established, she says.
References
1. Beral V, Bull D, Doll R, et al. Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83,000 women with breast cancer from 16 countries. Lancet 2004; 363:1,007-1,016.
2. National Cancer Institute. "Summary Report: Early Reproductive Events and Breast Cancer Workshop." Bethesda, MD; March 4, 2003. Accessed at: www.cancer. gov/cancerinfo/ere-workshop-report.
3. ACOG Committee on Gynecologic Practice. ACOG Committee Opinion. No. 285, August 2003: Induced abortion and breast cancer risk. Obstet Gynecol 2003; 102:433-435.
4. Gold RB. Review of key reproductive health-related developments in the states: 2003. Guttmacher Report on Public Policy 2003; 6:11-12.