Abortion and Breast Cancer: A Moral Position as a Conflict of Interest

by Jane Sprague Zones

Every so often BCA receives letters such as the one from Laura Piatkowski (below), calling us to task for not informing our members of an increased risk of breast cancer from induced abortion. The U.S. right-to-life movement has taken up breast cancer risk as further reason for women to shun abortion, and in recent years there have been advertising campaigns on radio and public transit claiming that abortion greatly increases the risk of breast cancer.

Posters in the transit systems of five major east coast cities, in a campaign sponsored by Christ’s Bride Ministries several years ago, declared that abortion causes “more and deadlier breast cancer.” The posters referred readers to a toll-free number, where at least one operator claimed that teenagers having abortions increase their risk of developing breast cancer by 800 percent, a number for which there is no evidence whatsoever. The National Women’s Health Network, a sister organization to BCA, campaigned effectively for these misleading signs to be removed.

The anti-abortion movement has also lobbied legislators to pass laws requiring physicians and other providers to inform women seeking abortion that the procedure will increase their risk of breast cancer. Such laws have been passed in Montana and Mississippi, and they are pending in 15 other states. Several lawsuits have also been filed based on the alleged link between abortion and breast cancer.

Does abortion increase breast cancer risk? The short answer is that there is no clear evidence one way or the other. There is a biologically plausible argument that breast cell differentiation during the latter half of pregnancy, which prepares the body for lactation, has lasting effects upon the cellular structure of the breast that is thought to reduce breast cancer risk. Mid-pregnancy interruption of the hormone surge that is the engine for this differentiation process has been hypothesized to increase the risk of breast cancer, because breast cancer originates in undifferentiated cells, but this theory has not been proven.

Many studies have been done in an effort to determine whether there is an abortion-related risk for breast cancer and, if so, how large a risk. Most of the research employs a “case-control” design: researchers match women who have been diagnosed with breast cancer with women who have not (usually matched by general age), and then compare the proportion of each group who report having had an abortion.

Case-control studies rely on participants to report on their abortion history, which is notoriously inaccurate. One study that appeared in the American Journal of Public Health last fall found significant underreporting (35 to 60 percent of actual abortions) in surveys.¹ Underreporting is more extreme in areas where there is strong social stigma around abortion, such as conservative Catholic regions.² Women with breast cancer are 50 percent more likely to report accurate abortion history,³ presumably because of their desire to understand potential origins of their disease. Because of this reporting bias, results are skewed in a way that makes it seem that women with breast cancer have a higher rate of abortion.

One of the best case-control studies found a 50 percent increased risk of breast cancer in women under age 45 who’d had an abortion.⁴ Because of the likelihood of reporting bias, the researchers called for further studies, stating that their study’s limitations “argue against a firm conclusion at this time.”

”Cohort” studies compare women who have had abortions with those who have not, following them for long periods of time to determine which group has a higher rate of breast cancer diagnosis. Because these studies do not rely on self-reported history, they are considered more valid than case-control studies. However, they take much longer and are therefore very expensive. No cohort study has found a relationship between abortion and breast cancer.

The most respected of the cohort studies on abortion and breast cancer risk is one done in Denmark, where the government keeps a health record for each citizen. Using data from national registries on abortion and on breast cancer for 1.5 million Danish women, researchers found no increased risk of breast cancer among those with a history of abortion.⁵

Three meta-analyses, which examine the collected findings from a number of studies, have also reported contradictory results. The three were published within four months of each other, between September 1996 and January 1997. One reviewed 19 studies, another 32; both found the collective research inadequate to determine with confidence the relationship between abortion and breast cancer.^6,7 If such a relationship exists, it is likely to be small.

The third meta-analysis, one often cited by the right-to-life movement, was done by Joel Brind and colleagues. Brind is a professor of biology and endocrinology at Baruch College, at the City University of New York. He and three colleagues from the Pennsylvania State College of Medicine published a meta-analysis of 23 studies and concluded that abortion increases the risk of cancer by 30 percent.⁸ The researchers’ analysis dismissed the validity of reporting bias, and their article has been strongly criticized because of assumptions made about a causal relationship between abortion and breast cancer. (A correlation between two events does not mean that one is responsible for causing the other.)

Brind, an active spokesperson for the National Right to Life movement for the past decade, is a frequent columnist in the National Right to Life News and a contributor to the National Review, a conservative political periodical. Although he has not published epidemiological research of his own design on this topic, he has been active in promoting his perspective that abortion is a significant cause of breast cancer. He is also the president of the Breast Cancer Prevention Institute, an organization that promotes this point of view.

Conflicts of Interest

BCA has frequently had cause to criticize research in which the funders or scientists had a vested interest in the outcome. It is well established, for example, that drug studies funded by pharmaceutical companies are much more likely to report positive drug effects than research carried out independently. Virtually all conflicts of interest in research have been related to industrial or professional profit. For instance, the Tobacco Institute, the research arm of major cigarette manufacturers, argued for decades that smoking did not increase the risk of lung cancer, despite the weight of evidence to the contrary.

In the case of abortion, the conflict of interest appears to be ideological rather than financial. Positions on abortion access in the United States have hardened to the extremes over the nearly three decades in which abortion has been legally available. It is difficult to sort out what role these resolute positions may play in conducting and publishing research. We should all be wary of absolute or extreme statements about the relationship between abortion and breast cancer.

Future research should determine the effect of a number of factors on breast cancer incidence: age at the time of abortion, whether the woman has carried another child to term, the stage of pregnancy at which abortion occurs, and differences between induced abortion and miscarriage.

Karin Michels, an epidemiologist at the Harvard School of Public Health, is currently working on a well-designed study of 700,000 American women that will factor in age and other confounding variables; she expects to finish her research in the fall. For the time being, it appears most sensible to take a wait-and-see approach on this issue, to encourage prospective studies, to refrain from making policy on the basis of a possible relationship, and to support all efforts to assist women in preventing unwanted pregnancies before conception.

The following letter, which BCA received via e-mail last fall, is an exact copy of the original, reprinted in full with permission from the writer.

Dear Editor: I find it a little strange that you, as an organization, purports to want to help women avoid breast cancer would discount the factor that explains the 70% of unexplained risks. That factor is ABORTION. You are so caught up in denying abortion as a risk factor that you have doomed more women to death. Why is your organization advocating the use of Tamoxifen and RU 486? They have proven they increase the risk for breast cancer. What is it about abortion that makes it sacrosanct that you do not consider its effect on your bodies? Why do you prize as a right the right to destroy your own child? I am told that I am very blunt when I speak and do not apologize for that. I just need to know the answers to those questions as well as the following. Why are you afraid to admit your need to control your body is given over to doctors, lovers and drug companies? When you can honestly answer these questions, maybe I can believe that you really are concerned with the health of women.

Laura Piatkowski
Brampton, Ontario, Canada

¹Jagannatha, Radha, “Relying on Surveys to Understand Abortion Behavior,” American Journal of Public Health, November 2001, vol. 91, no. 11, pp. 1825-31.

² Rookus, Matti A., and Flora E. van Leeuwen, “Induced Abortion and Risk for Breast Cancer: Reporting (Recall) Bias in a Dutch Case-Control Study.” Journal of the National Cancer Institute, December 4, 1996, vol. 88, no. 23, pp. 1759-64.

³ Lindefors-Harris, Britt-Marie, et al., “Response Bias in a Case-Control Study: Analysis Utilizing Comparative Data Concerning Legal Abortions from Two Independent Swedish Studies,” American Journal of Epidemiology, vol. 134, no. 9, 1991, pp. 1003-07.

⁴ Daling, Janet R., et al., “Risk of Breast Cancer Among Young Women: Relationship to Induced Abortion,” Journal of the National Cancer Institute, November 2, 1994, vol. 86, no. 21, pp. 1584-92.

⁵ Melbye, Mads et al., “Induced Abortion and the Risk of Breast Cancer.” New England Journal of Medicine, January 9, 1997, vol. 336, no. 2, pp. 81-85.

⁶ Michels, Karin B., and Walter C. Willett, “Does Induced or Spontaneous Abortion Affect the Risk of Breast Cancer?” Epidemiology, September 1996, vol. 7, no. 5, pp. 521-28.

⁷ Wingo, Phyllis A. et al., “The Risk of Breast Cancer Following Spontaneous or Induced Abortion.” Cancer Causes and Control, January 1997, vol. 8, no. 1, pp. 93-108.

⁸ Brind, Joel, et al., “Induced Abortion as an Independent Risk Factor for Breast Cancer: A Comprehensive Review and Meta-Analysis,” Journal of Epidemiology and Community Health, November 1996, vol. 50, no. 5, pp. 481-96.