The abortion–breast cancer hypothesis posits that having an induced abortion can increase the risk of getting breast cancer. This hypothesis is at odds with mainstream scientific opinion and is rejected by major medical professional organizations; despite this, it continues to be widely propagated as pseudoscience, typically in service of an anti-abortion agenda.

In early pregnancy, hormone levels increase, leading to breast growth. The hypothesis proposes that if this process is altered by an abortion, then more immature cells could be left behind, and that these immature cells could increase the risk of breast cancer over time.

The abortion–breast cancer hypothesis has been the subject of extensive scientific inquiry, and the scientific community has concluded that abortion does not cause breast cancer; the U.S. National Cancer Institute, the American Cancer Society, the American Congress of Obstetricians and Gynecologists, the Royal College of Obstetricians and Gynaecologists, the German Cancer Research Center, and the Canadian Cancer Society.

Some anti-abortion activists have continued to advance a discredited causal link between abortion and breast cancer. In response to public concern over this intervention, the NCI convened a 2003 workshop bringing together over 100 experts on the issue. This workshop concluded that while some studies reported a statistical correlation between breast cancer and abortion, the strongest scientific evidence from large prospective cohort studies demonstrates that abortion is not associated with an increase in breast cancer risk, and that the positive findings were likely due to response bias.

The ongoing promotion of a link between abortion and breast cancer is seen by others as part of the anti-abortion "woman-centered" strategy against abortion. a concern shared by some politically conservative politicians. The abortion–breast cancer issue remains the subject of political controversy.

Views of medical organizations

Major medical organizations which have analyzed data on abortion and breast cancer have uniformly concluded that abortion does not cause breast cancer. These organizations include the World Health Organization, the U.S. National Cancer Institute, the American Cancer Society, the American Congress of Obstetricians and Gynecologists, the Royal College of Obstetricians and Gynaecologists, the German Cancer Research Center, and the Canadian Cancer Society.

  • The U.S. National Cancer Institute, which is part of the National Institutes of Health, found that "induced abortion is not associated with an increase in breast cancer risk", assigning this conclusion the strongest possible evidence rating. The college recommended in its official clinical practice guidelines that "Women should be informed that induced abortion is not associated with an increase in breast cancer risk."
  • The German Cancer Research Center concluded in 2013 that abortion and miscarriage pose no risk of breast cancer. is the primary advocate of an abortion–breast cancer ("ABC") link. Brind is strongly anti-abortion and began lobbying politicians with the claim that abortion caused breast cancer in the early 1990s. arguing that induced abortion was a risk factor for breast cancer. The amount of attention the study received prompted a cautionary editorial by a JECH editor. With the appearance of larger studies contradicting Brind's finding, Brind failed to convince the scientific community that abortion caused breast cancer. In 2003, Brind was invited to the NCI workshop on abortion and breast cancer, where he was the only one to formally dissent from the workshop's finding that there is no link between the two. Brind blames the lack of support for his findings on a conspiracy, arguing that the NCI and other major medical organizations are engaged in a "cover-up" for the purpose of "protecting the abortion industry".

Breast tissue contains many lobes (segments) and these contain lobules which are groups of breast cells. There are four types of lobules:

  • Type 1 has 11 ductules (immature)
  • Type 2 has 47 ductules (immature)
  • Type 3 has 80 ductules (mature, fewer hormone receptors)
  • Type 4 are fully matured (cancer resistant) and contain breast milk

During early pregnancy, type 1 lobules quickly become type 2 lobules because of changes in estrogen and progesterone levels. Maturing into type 3 and then reaching full differentiation as type 4 lobules requires an increase of human placental lactogen (hPL) which occurs in the last few months of pregnancy. According to the abortion–breast cancer hypothesis, if an abortion were to interrupt this sequence then it could leave a higher ratio of type 2 lobules than existed prior to the pregnancy. Russo and Russo have shown that mature breast cells have more time for DNA repair with longer cell cycles, Bernstein et al. independently observed a reduced breast cancer risk when women were injected with hCG for weight loss or infertility treatment. Contrary to the ABC hypothesis, Michaels et al. hypothesize since hCG plays a role in cellular differentiation and may activate apoptosis, as levels of hCG increase early on in human pregnancy, "an incomplete pregnancy of short duration might impart the benefits of a full-term pregnancy and thus reduce the risk of breast cancer." Research relevant to the current ABC discussion focuses on more recent large cohort studies, a few meta-analyses, many case-control studies, and several early experiments with rats.

Rat models

Russo & Russo from the Fox Chase Cancer Center in Philadelphia conducted a study in 1980 examining the proposed correlation between abortion and breast cancer. While analysing the effects of the carcinogen 7,12-Dimethylbenz(a)anthracene (DMBA) on the DNA labeling index (DNA-LI) in terminal end buds (TEBs), terminal ducts (TDs) and alveolar buds (ABs) of Sprague-Dawley rats in various stages of reproductive development, they found that rats who had interrupted pregnancies had no noticeable increase in risk for cancer.

Despite the fact that the Russos' studies found similar risk rates between virgin and pregnancy interrupted rats, their research would be used to support the contention that abortion created a greater risk of breast cancer for the next twenty years. However, because rats do not exhibit naturally occurring breast cancer, the extrapolation of these results to human abortion and breast cancer is viewed as dubious.

Epidemiological evidence

The results of prospective cohort studies on the relationship between abortion and breast cancer have been consistently negative. Such studies are considered more reliable than retrospective studies and case-control studies. The positive association between abortion and breast cancer risk observed in case-control studies may be accounted for by recall bias.

In 1996, Brind et al. published a meta-analysis of 23 studies which reported a positive association existed between induced abortion and breast cancer risk. The authors estimated the relative risk of breast cancer among women who had had an induced abortion to be 1.3, compared to women who had not had an abortion. It was criticized by other researchers for multiple reasons, including allegations that it failed to account for publication bias (positive studies tend to be more likely to be published). The meta-analysis was also criticized because the studies it included were almost all case-control studies, which are susceptible to recall bias, and for which it is difficult to select an appropriate control group.

In 1997, Wingo et al. reviewed 32 studies on the abortion-breast cancer relationship and concluded that the results of studies on this subject were too inconsistent to allow for definitive conclusions, for either induced or spontaneous abortions.

A 2004 analysis of data from 53 studies involving 83,000 women with breast cancer reported no increased risk among women who had had either an induced or spontaneous abortion. The relative risk of breast cancer for women who had a spontaneous abortion in this analysis was 0.98, and that for induced abortion was 0.93.

A 2015 systematic review and meta-analysis of prospective studies found insufficient evidence to support an association between induced or spontaneous abortion and an increased risk of breast cancer.

Politicization

By the late 1980s, national politicians recognized that a focus on reducing access to abortion was not a winning political strategy. Some anti-abortion activists grew more aggressive and violent in the face of political abandonment, culminating with the murder of Dr. David Gunn in 1993 and the passage of the Freedom of Access to Clinic Entrances Act in 1994. With direct action discredited, anti-abortion organizations, including the National Right to Life Committee, came to the forefront of the movement. These focused on legal tactics, including lobbying against late-term abortions and access to mifepristone and demanding legislation based on the purported ABC link. and some feel that anti-abortion advocates treat ABC as simply another tactic in their campaign against abortion. There have been ongoing and incremental legal challenges to abortion in the United States by anti-abortion groups. In 2005, a Canadian anti-abortion organization put up billboards in Alberta with large pink ribbons and the statement: "Stop the Cover-Up", in reference to the ABC hypothesis. The Canadian Breast Cancer Foundation was concerned by the misrepresentation of the state of scientific knowledge on the subject.

The continued focus on the ABC hypothesis by anti-abortion groups has fostered a confrontational political environment. Anti-abortion advocates and scientists alike have responded with criticisms.

During the late 1990s, several members of the United States Congress became involved in the ABC issue. In a 1998 hearing on cancer research, U.S. Representative Tom Coburn accused the National Cancer Institute of misleading the public by selectively releasing data. In 1999, shortly after the House debated FDA approval of the abortion drug mifepristone, U.S. Representative Dave Weldon wrote a "Dear Colleague" letter, enclosing an article from John Kindley. Similar legislation requiring notification has also been introduced in 14 other states. An editor for the American Journal of Public Health expressed concern that these bills propose warnings that do not agree with established scientific findings.

Bioethicist Jacob M. Appel argues that the mandatory disclosure statutes might be unconstitutional on "rational basis" grounds. Childbirth is significantly more dangerous than abortion, data that is not required in any disclosure law but which is necessary for a meaningful understanding of risks. According to Appel, "[i]f the roughly fifty million abortions that have occurred in the United States since Roe v. Wade had all ended in full-term deliveries, approximately five hundred additional women would have died during childbirth."

In May 2017, President Donald Trump appointed Charmaine Yoest, an anti-abortion activist and proponent of the abortion-breast cancer link, to the post of assistant secretary for public affairs in the Department of Health And Human Services.

National Cancer Institute

The National Cancer Institute (NCI) has been a target of the anti-abortion movement for the conclusions presented on its website. In response to the alteration the NCI convened a three-day consensus workshop entitled Early Reproductive Events and Breast Cancer on 24–26 February 2003. The workshop concluded that induced abortion does not increase a woman's risk of breast cancer, and that the evidence for this had been well established. He contends the workshop evidence and findings were overly controlled by its organizers and that the time allotted was too short for a thorough review of the literature. The suit, Kjolsrud v. MKB Management Corporation, alleged that the clinic was misleading women by distributing a brochure quoting a National Cancer Institute fact sheet on the ABC hypothesis. The brochure stated:

The case was originally scheduled for 11 September 2001, but was delayed as a result of the terrorist attacks. On 25 March 2002, the trial began. After four days of testimony, Judge Michael McGuire ruled in favor of the clinic. John Kindley, one of the lawyers representing Kjolsrud, highlighted the "individual's right to self-determination". Kindley also wrote a 1998 Wisconsin Law Review article outlining the viability of medical malpractice lawsuits based upon not informing patients considering abortion about the ABC hypothesis.

The decision was appealed and on 23 September 2003 the North Dakota Supreme Court ruled that Kjolsrud did not have standing and affirmed the lower court ruling dismissing the action.

References

  • National Cancer Institute: Abortion, Miscarriage, and Breast Cancer Risk
  • Induced abortion does not increase breast cancer risk, a fact sheet from the World Health Organization
  • Abortion and Breast Cancer Risk from the American Cancer Society
  • American College of Obstetricians and Gynecologists: Finds No Link Between Abortion and Breast Cancer Risk
  • The Care of Women Requesting Induced Abortion, from the Royal College of Obstetricians and Gynaecologists
  • Discover Magazine: The Scientist Who Hated Abortion by Barry Yeoman
  • Factors That Do Not Increase Risk from the Susan G. Komen Foundation