No link found between abortion, breast cancer

Epidemiological evidence presented at a recent Bethesda, MD-based National Cancer Institute (NCI) workshop could help end a longstanding debate on the question of induced abortion and risk of breast cancer.

"Our studies did not find breast cancer risk to be increased overall or in any subgroups of women, defined by age at the time of the abortion or by length of gestation when the abortion occurred," states Leslie Bernstein, PhD, senior associate dean at the University of Southern California in Los Angeles, who presented information at the workshop. "Concern had been expressed previously regarding some subgroups defined by age and gestational length."

Outcomes of the meeting were reviewed by the NCI’s Board of Scientific Advisors and Board of Scientific Counselors, which has since issued a report summarizing the epidemiologic, clinical, and animal studies findings related to early reproductive events and breast cancer risk. According to the report, the evidence showing that induced abortion is not associated with an increase in breast cancer risk is well established.1

The workshop was convened after dissension arose following the posting of a revised fact sheet on the NCI web site, www.cancer.gov. The federal agency, which offers information on cancer detection, prevention, and treatments for consumers and health professionals, first developed a fact sheet on the question of abortion and breast cancer in October 1994.2 The fact sheet, which has been revised six times, had stated that studies showed "no association between abortion and breast cancer." In November 2002, however, the fact sheet was revised to state the evidence for a link between induced abortions and breast cancer was inconclusive.3

A new fact sheet containing the workshop’s findings had just been posted, says Mary Anne Bright, acting deputy director of the NCI office of communications.

Review the evidence

Why have some researchers linked abortion with an increased risk for breast cancer? According to information from the New York City-based Planned Parenthood Federation of America, such a belief has been linked to the hormonal disruption that occurs when a woman’s pregnancy is terminated. Some researchers have claimed that interruption of the first trimester of a first pregnancy causes a cessation of cell differentiation that may result in a subsequent increase in the risk of cancerous growth in these tissues; attempts to prove this theory, however, have failed.

At the February 2003 workshop, participants reviewed evidence on all aspects of pregnancy in relation to breast cancer risk. Bernstein presented new data from three large studies showing no increase in breast cancer risk in association with having an abortion. Two of the studies are unpublished; one has just been published in the journal Cancer Epidemiology Biomarkers & Prevention.5

The studies did not find breast cancer risk to be increased overall or in any subgroups of women, defined by age at the time of the abortion or by length of gestation when the abortion occurred, says Bernstein. Concern had been expressed previously regarding some subgroups defined by age and gestational length, she notes.

An important issue in the statistical analysis of such studies is whether women who have never had a term pregnancy but have been pregnant are compared to women who have had term pregnancies, observes Bernstein. Such an approach does not address the question, "does an induced abortion increase breast cancer risk?" and could lead to incorrect conclusions, she notes.

"In our analyses, we assessed whether biased reporting might have occurred; we found no evidence of any underreporting of an induced abortion by women who served as controls in the two case-control studies," states Bernstein. "Such under-reporting generally leads to elevated estimates of breast cancer risk when none actually exists, and this is a likely explanation for some of the studies in which an association was reported."

Additional data were presented in the closed session of the workshop, which extended results from an earlier study of 1.5 million Danish women.6 The original study showed no overall effect on the risk of breast cancer and induced abortion; the follow-up evidence strengthened the original findings, says Bernstein.

Following the presentations, scientists discussed the state of the evidence, crafted statements regarding the evidence, and assigned the statements a numeric code that indicated the level of certainty, says Bernstein. It was concluded that induced abortion is not associated with an increased risk of breast cancer, she notes.

Other findings eyed

The panel also accepted several other findings, including the following:

  • Early age at first-term birth is related to lifetime decrease in breast cancer risk.
  • Increasing parity is associated with a long-term risk reduction, even when controlling for age at first birth.
  • The additional long-term protective effect of young age at subsequent term pregnancies is not as strong as for the first-term pregnancy.
  • Breast cancer risk is transiently increased after a term pregnancy.
  • Recognized spontaneous abortion is not associated with an increase in breast cancer risk.
  • Long duration of lactation provides a small additional reduction in breast cancer risk after consideration of age at and number of term pregnancies.

References

1. 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.

2. Squires S. Study discounts link between abortion, breast cancer risk. Washington Post; Feb. 28, 2003; A11.

3. Altman LK. Panel finds no connection between cancer and abortion. New York Times; March 7, 2003. Accessed at www.nytimes.com/2003/03/07/health/07ABOR.html.

4. Planned Parenthood Federation of America. Anti-Choice Claims About Abortion and Breast Cancer. New York City. Accessed at www.plannedparenthood.org/library/facts/fact_cancer_022800.html.

5. Mahue-Giangreco M, Ursin G, Sullivan-Halley J, et al. Induced abortion, miscarriage, and breast cancer risk of young women. Cancer Epidemiology Biomarkers & Prevention 2003; 12:209-214.

6. Melbye M, Wohlfahrt J, Olsen JH, et al. Induced abortion and the risk of breast cancer. N Engl J Med 1997; 336:81-85.