Abortion–breast cancer hypothesis
The abortion–breast cancer hypothesis posits that having an induced abortion can increase the risk of getting breast cancer.[1] This hypothesis is at odds with mainstream scientific opinion and is rejected by major medical professional organizations;[1][2] 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.[3] 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.[4]
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;[1][2] and that breast cancer should not be a concern for women who are having a miscarriage or considering having an abortion. This consensus is supported by major medical bodies,[5] including the World Health Organization,[6][7] the U.S. National Cancer Institute,[8][9] the American Cancer Society,[10] the American Congress of Obstetricians and Gynecologists,[11] the Royal College of Obstetricians and Gynaecologists,[12] the German Cancer Research Center,[13] and the Canadian Cancer Society.[14]
Some anti-abortion activists have continued to advance a discredited causal link between abortion and breast cancer.[5] In the United States, they have advanced state legislation that in several states requires health care providers to present abortion as a cause of breast cancer when counseling women who are seeking abortion.[15] This political intervention culminated when the George W. Bush administration altered the National Cancer Institute website to suggest that abortion might cause breast cancer.[16] 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,[17][18][19] the strongest scientific evidence[20] from large prospective cohort studies[21][22] demonstrates that abortion is not associated with an increase in breast cancer risk,[23] and that the positive findings were likely due to response bias.[24]
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.[25][26][27] Anti-abortion groups maintain they are providing information necessary for legally required informed consent,[28] a concern shared by some politically conservative politicians.[29] The abortion–breast cancer issue remains the subject of political controversy.[5]
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.[6][11][12][13][14][23]
Proponents[edit]
Joel Brind, a faculty member at Baruch College in the Department of Natural Sciences,[34] 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.[35] Brind found that his lobbying efforts were not taken seriously because he had not published his findings in the peer-reviewed medical literature. He therefore collaborated with two anti-abortion physicians and a statistician to publish a 1996 article in the Journal of Epidemiology and Community Health,[36] arguing that induced abortion was a risk factor for breast cancer.[35] The statistician who collaborated with Brind later stated of their findings: "I have some doubts. I don't think the issue has been resolved. When we were talking about the conclusions, he [Brind] wanted to make the strongest statements. I tried to temper them a little bit, but Dr. Brind is very adamant about his opinion."[35]
Brind's paper was criticized in the Journal of the National Cancer Institute for ignoring the role of response bias and for a "blurring of association with causation."[37] The amount of attention the study received prompted a cautionary editorial by a JECH editor.[38] 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".[35]
In early pregnancy, levels of estrogen, progesterone, and estradiol increase, leading to breast growth in preparation for lactation. Proponents speculate that if this process is interrupted by an abortion or miscarriage—before full maturity (differentiation) in the third trimester—then more immature cells could be left than there were prior to the pregnancy. These immature cells could then be exposed to carcinogens and hormones over time, resulting in a greater potential risk of breast cancer. This mechanism was first proposed and explored in rat studies conducted in the 1980s.[39][40][41]
Breast tissue contains many lobes (segments) and these contain lobules which are groups of breast cells. There are four types of lobules:
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.[42] Russo and Russo have shown that mature breast cells have more time for DNA repair with longer cell cycles,[43] accounting for the slightly reduced risk of breast cancer for parous women against the baseline risk for women who have never conceived and those who have conceived and terminated their pregnancies.[39]
Later on, Russo et al. found that placental human chorionic gonadotropin (hCG) induces the synthesis of inhibin by the mammary epithelium.[44][45] Bernstein et al. independently observed a reduced breast cancer risk when women were injected with hCG for weight loss or infertility treatment.[46] 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."[22]
Epidemiological evidence[edit]
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.[49][50] The positive association between abortion and breast cancer risk observed in case-control studies may be accounted for by recall bias.[51]
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.[52] 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).[53] 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.[54]
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.[55]
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.[56]
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.[57]