Abortion–breast cancer hypothesis

The abortion-breast cancer (ABC) hypothesis (also known as ABC link) posits a causal relationship between induced abortion and an increased risk of developing breast cancer. The hypothesis has not been verified and abortion is not considered an actual breast cancer risk by any major cancer organization.

In early pregnancy the level of estrogens increase and initiates breast growth in preparation for lactation. The ABC hypothesis proposes that if this process is interrupted with an abortion – before full differentiation in the third trimester – then more relatively vulnerable undifferentiated cells could be left than there were prior to the pregnancy, resulting in a greater potential risk of breast cancer.

A large epidemiological study done by Dr. Mads Melbye et al. in 1997, with data from two national registries in Denmark, reported the correlation to be negligible to non-existent after statistical adjustment. The National Cancer Institute conducted an official workshop with numerous experts on the issue in February 2003, which concluded with its highest strength rating for the selected evidence it considered that "induced abortion is not associated with an increase in breast cancer risk." Then in 2004, Dr. Beral et al. published a collaborative reanalysis of 53 epidemiological studies and concluded that abortion does "not increase a woman's risk of developing breast cancer."

Of over 100 experts at the NCI workshop, Dr. Joel Brind, ABC's primary advocate and an invitee to the workshop, filed the only dissenting opinion which criticized the NCI and Melbye conclusions. Brind points out the majority of interview-based studies have indicated a link, and some have been demonstrated to be statistically significant, but there remains debate as to their reliability because of possible response bias. Most medical professionals agree with the recent research that concludes no ABC association, and the ABC issue is seen by some as merely a part of the current pro-life "woman centered" strategy against abortion. Nevertheless, gaps and inconsistencies remain in the research, and the subject continues to be one of mostly political but some scientific contention.

NCI workshop

The National Cancer Institute (NCI) conducted a workshop to evaluate the scientific evidence regarding the ABC hypothesis. This was done in response to alterations to the NCI website by the Bush administration in November 2002. [1] The workshop concluded that the evidence was well established against an abortion increasing a woman's risk of breast cancer. [2] It has been reported the workshop largely used the Denmark (1997) study to reach their conclusions despite contradictory results within it, which during the workshop Dr. Melbye stated he had "reanalyzed" the data and the 89% increased risk is "no longer present in his research." [3] Some organizations have changed their position to be in line with the NCI workshop findings.

Dr. Brind was invited to the workshop and he alleges the chairperson exercised "major" control over who was to be invited, and many of the invited scientists were dependent on the NCI or other federal agencies for grants. [4] The main expert who made the formal ABC presentation primarily had expertise in obesity and exercise in relation to breast cancer. Dr. Daling, who had published on the ABC issue, was asked to present on another topic. Preterm delivery was listed as an epidemiological "gap" even though there was evidence of a correlation with higher breast cancer risk. [5] No minority or dissenting report was requested but Dr. Brind did file a dissenting opinion. [6]

Pro-life bias

When pro-life advocates link abortion to breast cancer, some claim that the goal is to stop women from having an induced abortion. Because breast cancer elicits disproportionate fear in women,[7] there exists the concern that pro-lifers use it as scare tactic. ABC advocates who oppose abortion have been accused of focusing on positive and/or averaged results, ignoring caveats and low-risk subgroups. These advocates rebut by stating that their ABC information is for the benefit of women's health and to provide informed consent, but they ignore potentially higher and more immediate health risks associated with pregnancy.

At the same time pro-lifers lobby to increase obstacles to abortion (such as mandated counseling, waiting periods, and parental notification) [8], and some feel that pro-lifers treat ABC as simply another weapon in their arsenal. In enacting these obstacles it takes longer for a women to get an abortion; and as a result this increases the risk of complications. The ongoing and incremental legal challenges to abortion by pro-life groups is documented in Frontline's The Last Abortion Clinic.

See Breast Cancer: Its Link to Abortion and the Birth Control Pill by Chris Kahlenborn, MD (ISBN 0966977734) for an extended argument from the pro-life perspective.

Scientific studies

Scientific research on ABC has used including testing of rats, interviews (case-control), meta-analysis and cohorts. ABC studies have been conducted since 1957, [9] but this covers recent ABC research history, starting with the large cohort studies and then finishing in 1980 with the first rat study.

The majority of the results in epidemiologic scientific studies are calculated as a relative risk with 1.0 being 0% and a (95% confidence interval). This means a relative risk of 1.51 (0.93-1.87) is a 51% increased risk with a 95% chance that the actual risk is within the range given. With more data, the confidence interval becomes smaller, making it an indicator of the result's statistical reliability.

Confounding factors and hormones

There are many confounding factors for breast cancer. Genetics is a major factor which plays a role in the long list of socioeconomic factors. As Western society has modernized confounding factors such as environmental carcinogens, delayed child rearing, less breastfeeding, hormone replacement therapy (HRT), oral contraceptives, early menarche and obesity have increased. If these were not accounted for, they would obscure any effect an individual factor (like abortion) would have. As such they need to be removed using controls – a woman who is very similar to another woman with the exception of an abortion – otherwise you could get a false positive or negative result based on another factor. Examining the ABC issue is all the more difficult because induced abortions have increased during the same period. [10] Premature birth adds further complications since an uncorroborated study has indicated it is associated with a history of induced abortion [11] and higher breast cancer risk. [12]

One of the most significant controllable factors is parity, or the number of children a women has given birth to prior to the abortion. With each pregnancy (particularly the first) the breasts undergo growth and differentiation; consequently having no children can increase breast cancer risk. All of these confounding factors have an effect, directly or indirectly, on hormones which impact breast cancer risk; but they do not significantly affect the results of ABC studies that are properly conducted and take these factors into account with case-control matching.

• Steroidal estrogen added to the federal carcinogen list in December 2002. [13]
• A Women's Health Initiative HRT study cut short from an elevated breast cancer risk using estrogen with progestin. [14]
• The American Cancer Society (ACS) [15] and the National Cancer Institute (NCI) [16] note reproductive hormones can elevate breast cancer risk.

The controversial nature of abortion may introduce response bias into interview studies; especially for studies done in decades past when abortion was less accepted. In the late 20th century there was some concern of an increase of breast cancer incidence. This was found to be partly due to women living longer, and better detection methods finding breast cancer earlier. [17] It should be noted the overall incidence does not effect ABC studies with proper controls because the case and control subjects would be equally affected.

Cohorts

Melbye

A large, highly regarded ABC study was published by Dr. Melbye et al. (1997) [18] of the Statens Serum Institute in Copenhagen, had 1.5 million Danish women in the database (1,338 breast cancer cases – 8,908 controls). Of those, 280,965 women had induced abortions recorded in the computerized registry, which was started in 1973 when having an induced abortion through 12 weeks was fully legalized. The relative risk after statistical adjustment came to 1.00 (0.94 to 1.06). This led to the conclusion that "induced abortions have no overall effect on the risk of breast cancer." The Melbye study's conclusions garnered great attention from the media and many organizations such as the NCI and Planned Parenthood, who use it as a foundation to argue that the best scientific evidence does not support an ABC link.

The Melbye study used women born from 1935 to 1978, but the computerized registry of induced abortions only started in 1973. As a result Dr. Brind found more than 30,000 women had been misclassified as having no abortion because the induced abortion occurred prior to 1973. [19] Dr. Melbye et al. responded that if the misclassified older women had their risk underestimated, it would be expected that the younger groups would have a higher risk. Their statistically adjusted relative risks indicated this was not the case. However, Drs. Brind and Chinchilli had concerns about the Melbye study database and how they statistically adjusted their overall relative risk.

In a large cohort study it is necessary to account for confounding factors that may have increased over time. For example, if the pill affected breast cancer rates 40 year old women in 1990 (young birth-cohort) would have a higher incidence of breast cancer than 40 year olds in 1970 (older birth-cohort), as the older cohort had little to no access to the pill during their reproductive years. Typically this is corrected by having case-control matching, but instead the Melbye study statistically adjusted out observed birth-cohort increases. Dr. Brind argues that Dr. Melbye et al. adjusted out induced abortion from the overall results because it is one of the confounding factors which has increased over the same time period, and the finding of exactly 1.00 agrees with that assertion. Dr. Melbye et al. found the point to be self-contradictory, considering Dr. Brind wanted birth-cohort matching, then argued against "taking birth-cohort differences into account." It is unclear how this is a contradiction, since Dr. Brind is against the use of just statistical adjustment, and in favor of case-control cohort matching to account for birth-cohort differences. [20]

Drs. Senghas and Dolan did not understand why a statistically significant result for induced abortions done after 18 weeks gestation was not in the results section of the Melbye study abstract. Dr. Melbye et al. explained that even though the result was in line with the hypothesis of Russo and Russo, they deemed the number of cancer cases small, and did not want to overstate the finding.

Here is the first section of Table 1 in the Melbye study:

Week of gestation	No. of Cancers	Person-Years (Thousands)	Relative Risk (95% CI)*	Multivariate Relative Risk (95% CI)†
<7	36	82	0.81 (0.58-1.13)	0.81 (0.58-1.13)
7-8	526	1012	1.01 (0.89-1.14)	1.01 (0.89-1.14)
9-10‡	534	1118	1	1
11-12	205	422	1.12 (0.95-1.31)	1.12 (0.95-1.31)
13-14	6	14	1.13 (0.50-2.52)	1.13 (0.51-2.53)
15-18	17	35	1.24 (0.76-2.01)	1.23 (0.76-2.00)
>18	14	14	1.92 (1.13-3.26)	1.89 (1.11-3.22)

*The relative risks were calculated separately for each of the five variables, with adjustment for women's age, calendar period, parity, and age at delivery of a first child. CI denotes confidence interval.
†Values were adjusted for women's age, calendar period, parity, age at delivery of a first child, and the other variables shown in the table.
‡The women with this characteristic served as the reference group.

Other sections listed age at induced abortion, number of induced abortions, time since induced abortion, and time of induced abortion and live-birth history. There was an indication of an elevated risk of 1.29 (0.80-2.08) for 12-19 year olds (relative to 20-24 subcohort), and a protective effect 0.74 (0.41-1.33) for women with an induced abortion before and after their first live birth (relative to induced abortion after 1st live birth subcohort).

Howe

The 1989 study [21] by Dr. Holly Howe et al. at the New York State Department of Health examined young women with breast cancer in upstate New York (1,451 breast cancer cases – 1,451 controls). The results indicated a significant 90% (1.2-3.0) increased risk for induced abortion, an insignificant 50% (0.7-3.7) increase for spontaneous abortion, and 300% (1.5-13.6) increase for multiple abortions with no intervening births. The authors believed that the study was inconclusive, but raised new questions for continuing research as women's recorded contraceptive histories grew.

The study is significant evidence that the positive ABC results in interview studies were not purely a result of response bias. According to Scott Somerville of Accuracy in Media it took a long time for Howe's study to be published due to a number of American journals that rejected the article. Eventually in Britain, the International Journal of Epidemiology published it in 1989. [22]

Lindefors-Harris

Another cohort study by Dr. Lindefors-Harris et al. (1989) [23] was done looking at 49,000 women who had received abortions before the age of 30 in Sweden (65 breast cancer cases – compared with estimate of occurrence in general population). Although reported by some sources as being a "large" cohort study the actual number of breast cancer cases is a fraction of most other studies. The risk for women who'd given birth previous to the abortion was 0.58 (0.38-0.84), whereas women with no births had an insignificant risk increase of 1.09 (0.71-1.56). Overall, the relative risk was 0.77 (0.58-0.99), making for a 23% reduced risk in comparison to "contemporary Swedish population with due consideration to age."

According to Scott Somerville, the Lindefors-Harris study is flawed because their control group isn't well defined. The study combines women both with and without children. It also makes no attempt to compensate for the fact most women in Sweden, unlike America, already have children at the time of abortion. Thus the protective effect seen in the study is likely from earlier pregnancies rather than abortion. Additionally a large part of the funding for the study came from "Family Health, International," which is allegedly a research arm of the abortion industry. [24]

Meta-analysis

Beral

In March 2004, Dr. Beral et al. published a study in The Lancet as a collaborative reanalysis on Breast cancer and abortion. [25] This meta-analysis of 53 epidemiologic studies of 83,000 women with breast cancer undertaken in 16 countries did not find evidence of a relationship between induced abortion and breast cancer, with a relative risk of 0.93 (0.89-0.96). Many organizations and media outlets have referenced it as the latest and most comprehensive overview of the ABC evidence. Dr. Brind disagrees with this assessment and believes it is subject to selection bias. He also questions how it could be a "collaborative reanalysis" when "internationally accepted standards of authorship" specify only the five authors of this study are responsible for its conclusions. [26]

Brind

A meta-analysis was conducted by Dr. Brind et al. (1997) with both pro-choice and pro-life scientists that examined 28 published studies. [27] It concluded that there was on average a 30% (1.2-1.4) increased risk of breast cancer. The meta-analysis was criticized for selection bias by using studies with widely varying results, not working with the raw data from several studies, and including some studies that have alleged methodological weaknesses. [28]

The Royal College of Obstetrics and Gynaecology in March 2000 published evidence-based guidelines on women requesting induced abortion. The review of the available evidence at the time was "inconclusive" regarding the ABC link. They also noted "Brind's paper had no methodological shortcomings and could not be disregarded." [29]

Interviews

Interview (case-control) based studies have been inconsistent on the ABC link. With the small numbers involved in each individual study and the possibility that recall bias skewed the results, recent focus has switched to meta-analysis and record based studies which are typically much larger. [30] Here are a few interview studies of note.

Daling

Dr. Daling from the Fred Hutchinson Research Center headed two studies on the ABC issue looking at women in Washington state. The 1994 study results indicated a 50% (1.2-1.9) increased risk. [31] This was reflected in higher risks for women younger than 18 or older than 30 years of age who have had abortions after 8 weeks' gestation. Their conclusion emphasized that although this study supported the ABC link, the overall results from epidemiologic studies are inconsistent.

The Daling study in 1996 resulted in a relative risk of 1.2 (1.0-1.5). [32] The risk was highest among women without children who had abortions prior to 9 weeks gestation. Dr. Daling et al. examined the possibility of response bias by comparing results from two recent studies on invasive cervical cancer and ovarian cancer. The results argued against significant response bias. The Rookus (1996) study [33] noted that patients with cervical cancer may report differently than breast cancer patients.

On September 28th, 1997 an interview with Dr. Daling was published by the Los Angeles Daily News. In it she made the following statement:

"I have three sisters with breast cancer and I resent people messing with the scientific data to further their own agenda, be they pro-choice or pro-life. I would have loved to have found no association between breast cancer and abortion, but our research is rock solid and our data is accurate."

Sanderson

A 2001 study [34] conducted in Shanghai, China by Dr. Sanderson from the University of South Carolina and South Carolina Cancer Center at Columbia concluded that there was no ABC link and that multiple abortions did not put one at greater risk. Since induced abortion is common, legal, and even mandated by the government in China, the recall bias was minimized. [35]

Critics of the Chinese studies have said that the same factors that make them ideal for reducing recall bias also makes them inappropriate for comparison to the West. [36] [37] With the wide availability of abortion services, over 80% of them were done within the first eight weeks of gestation. In comparison only 55% of American women had an abortion before the ninth week. [38] Due to China’s strict population control, the vast majority of the abortions in the Chinese study were done after the first full-term pregnancy, which had been relatively early. This is not reflected in North America.

Response bias

Response bias normally occurs when people with a disease over-report exposure to suggested risk factors. For instance CJD patients reported an astonishingly high level of veal consuption. It is unlikely that any woman would forget an abortion, and response bias must occurs= when women intentionally "underreport" their abortion history. Meaning they deny having an abortion or claim to have fewer abortions than they've actually had. This can happen because of the personal, and in some places controversial nature of abortion, some women may not want provide full disclosure. Furthermore, women in the control group are more likely to have no serious illnesses, and hence have less motivation to be truthful than those trying to diagnose their problem. If this occurred then it would artificially create an ABC link where none existed. Two major studies have been published examining abortion response bias.

A review of ABC studies was conducted by Grimes in 1998. It concluded that if studies least susceptible to response bias are considered, they suggest there is no ABC link. [39]

An editorial in the Journal of the National Cancer Institute examined the notion of epidemiology reaching its limit given the possibility of response bias putting results in doubt. It concluded: "Indeed, after this excursion into the issue of abortion, bias, and breast cancer, it seems our future has as much to do with human behavior as with human biology." [40] This not only commented on the patients in studies, but focused its attention on the potential biases of the researchers themselves.

Lindefors-Harris

The Lindefors-Harris (1991) study [41] was the first major study to examine response and recall bias. It used the data of two independent Swedish induced abortion studies, and concluded there was a 50% (1.1-2.1) margin of error due to recall bias. However, eight women (seven cases, one control) included in this error margin apparently "overreported" their abortions, meaning the women reported having an abortion that was not reflected in the records. It was decided that for the purposes of the study, these women did not have abortions.

Dr. Daling (1994) found it "reasonable to assume that virtually no women who truly did not have an abortion would claim to have had one," [42] and missing records could have occurred for a variety of reasons. With these eight women removed the error margin is reduced to 16% which severely limits its statistical significance. Dr. Brind believes the remaining 16% could have resulted from the Swedish fertility registry. [43] These women were interviewed as mothers, which could have increased the tendency to underreport, given that a mother might not want to appear unfit. [44] Subsequently the Lindefors-Harris obliquely retracted the 50% conclusion in 1998, [45] but reasserted since the Denmark (Melbye 1997) cohort study, [46] found no link the 30% increased risk in the Brind meta-analysis [47] must be the accumulative result of response bias.

Rookus

The Rookus (1996) study [48] compared two regions in the Netherlands to assess the effect of religion on ABC results based on interviews. The secular (western) and conservative (southeastern) regions showed ABC relative risks of 1.3 (0.7-2.6) and 14.6 (1.8-120.0) respectively. Although this was a large variance, Dr. Brind et al. pointed out [49] that it was attained with an extremely small sample size. (12 cases and 1 control)

Rookus et al. supported this finding with an analysis of how much recall bias existed with oral contraceptive use that could be verified through records. It corroborated the bias, but Brind's et al. letter clarifies it only indicated response bias between the two regions, not between case and control subjects within regions. Dr. Rookus et al. responded [50] to the criticism by noting that there was 4.5 month underreporting difference between control and case subjects in the conservative region. This is indirect evidence for reporting bias since comfort with reporting oral contraception should be higher than induced abortion.

Rookus et al. also acknowledged the weakness in the Lindefors-Harris (1991) study, but emphasized that more controls (16/59 = 27.1%) than case patients (5/24 = 20.8%) did not report registered induced abortions. They concluded that finding a causal ABC link would be a disservice to the public, and epidemiologic research if "bias has not been ruled out convincingly."

Rats

The Russo & Russo (1980) study [51] of the Fox Chase Cancer Center in Philadelphia found that rats who received abortions had a "similar or even higher incidence of benign lesions" and carcinomas than virgin rats of matching age. A more thorough examination of the phenomenon was conducted in 1982 [52], which confirmed the results. A later study in 1987 [53] further explained their previous findings. After differentiation of the mammary gland resulting from a full-term pregnancy of the rat, the rate of cell division decreases and the cell cycle length increases, allowing more time for DNA repair. [54]

In a Discover article sidebar [55] entitled Humans Are Not Rats, Dr. Gil Mor, the director of reproductive immunology at the Yale University School of Medicine, disagrees with Dr. Brind and Drs. Russo & Russo on the importance of the rat studies findings. Dr. Mor emphasizes that rat studies are ideal for understanding basic processes but it would be scientifically "wobbly" to extrapolate those findings to humans.

Spontaneous abortion

Studies of spontaneous abortions (miscarriages) have generally shown no increase in breast cancer risk, [56] although a study by Paolilli et al. concluded there is a "suggestion of increased risk" 1.2 (0.92 to 1.56) after 3 or more pregnancy losses. [57] Some argue that this apparent lack of effect of miscarriages on breast cancer risk is evidence against the ABC hypothesis, and some pro-choice advocates have claimed it is proof that neither early pregnancy loss nor abortion are risk factors for breast cancer. [58]

One of the problems with comparing miscarriage to abortion is the issue of hormone levels in early pregnancy, a key point because the ABC hypothesis rests on hormonal influence over breast tissue development. Given the association of most miscarriages with abnormally low hormone levels it may not be analogous to an induced abortion of a healthy pregnancy, and a definitive conclusion about ABC risk based on miscarriage data alone is probably unsupported. While it is true most miscarriages are not caused by low hormones, most miscarriages are characterized by low hormone levels. [59] One of the first studies on hormone levels and spontaneous abortion by Kunz & Keller (1976) [60] showed that when progesterone is abnormally low a miscarriage occurs 89% percent of the time. This is also reflected in studies published by Hertz et al. (1979) [61] and in more detail by Stewart et al. (1993). [62]

A distinction should also be made for second trimester miscarriages as their hormonal characteristics differ from first trimester miscarriages.

North Dakota lawsuit

In January of 2000 Amy Jo Kjolsrud (née Mattson), a pro-life counselor, sued the Red River Women's Clinic in Fargo, North Dakota alleging false advertising. The suit alleged the clinic was misleading women by distributing a brochure quoting a National Cancer Institute fact sheet on the ABC issue which stated:

"Anti-abortion activists claim that having an abortion increases the risk of developing breast cancer and endangers future childbearing. None of these claims are supported by medical research or established medical organizations." (emphasis in original) [63]

The case was originally scheduled for September 11th, 2001 but was delayed as a result of the terrorist attacks. On March 25, 2002 the trial started and after four days of testimony Judge Michael McGuire ruled in favor of the clinic. In his decision he said:

"It does appear that the clinic had the intent to put out correct information and that their information is not untrue or misleading in any way. They did exercise reasonable care... One thing is clear from the experts, and that is that there are inconsistencies. The issue seems to be in a state of flux."

The judge noted it was their "intent" to provide accurate information because the brochure used an outdated fact sheet. [64] Linda Rosenthal, an attorney from the Center for Reproductive Rights characterized the decision thusly: "The judge rejected the abortion-breast cancer scare tactic. This ruling should put to rest the unethical, anti-choice scare tactic of using pseudo-science to harass abortion clinics and scare women." [65] John Kindley, one of the lawyers representing Ms. Kjolsrud stated: "I think most citizens, whether they are pro-choice or pro-life, believe in an individual's right to self-determination. They believe people shouldn't be misled and should be told about [procedural] risks, even if there is controversy over those risks." [66] Kindley also wrote an article published in 1999 by the Wisconsin Law Review outlining the viability of medical malpractice lawsuits based upon not informing patients considering abortion about the evidence indicating an ABC link. [67]

The decision was appealed and on September 23rd, 2003 to the North Dakota Supreme Court which ruled the false advertising law [68] should not have been used by Ms. Kjolsrud. This was because she personally had suffered no injury and hence had no standing (according to North Dakota jurisprudence) to file the lawsuit on behalf of others. In the appeal, Ms. Kjolsrud "concedes she had not read the brochures before filing her action." [69] However, the appeal also noted that after the lawsuit was filed the abortion clinic updated their brochure to the following:

Some anti-abortion activists claim that having an abortion increases the risk of developing breast cancer. A substantial body of medical research indicates that there is no established link between abortion and breast cancer. In fact, the National Cancer Institute has stated, "[t]here is no evidence of a direct relationship between breast cancer and either induced or spontaneous abortion."

State laws

As of November 2004, women seeking abortions in Mississippi must first sign a form indicating they've been told abortion could increase their risk of breast cancer. In Texas, Louisiana, and Kansas, state law requires women receive a pamphlet that suggests a cancer link with abortion. Similar legislation requiring notification has also been introduced, and is pending, in 14 other states. [70] These state laws put up further barriers to elective abortion [71], and critics charge that they have the real potential to misinform women of the actual risks of the procedure. However, it is possible that such legally-mandated disclosure could mitigate possible future lawsuits involving informed consent [72] from women who might contend they should have been told of the ABC link possibility prior to having an abortion.

Conclusion

A vocal pro-life minority insist there is an ABC link, but no major international cancer organization considers abortion to be a breast cancer risk. The scientific consensus is that the evidence is inconclusive. [73] This is due to conflicting studies and even contradictory results within studies, which could be occurring because the effect being sought is too small, does not exist, and/or as a result incomplete data and flaws in the studies. However, any potential ABC association is minor when compared to established genetic and lifestyle risk factors for breast cancer. It is also worth considering that when a correlation is indicated the relative risk or the data is usually statistically insufficient to conclude a causal link according to epidemiological standards.

External links

Scientific

• NIH: Breast Cancer and the Politics of Abortion in the United States
• NCI: Abortion, Miscarriage, and Breast Cancer Risk
• ACS: What Are the Risk Factors for Breast Cancer?
• ACOG: Finds No Link Between Abortion and Breast Cancer Risk
• RCOG: What you need to know about Abortion Care PDF document

Pro-Choice

• PPFA: Anti-choice Claims About Abortion and Breast Cancer
• Religious Tolerance: Is There A Link Between Abortion And Breast Cancer?
• CRR: False Claims of Breast Cancer Risk
• Democrats.Reform.House.Gov – Politics and Science: Breast Cancer Risks
• Discover: The Scientist Who Hated Abortion by Barry Yeoman

Pro-Life

• Breast Cancer Prevention Institute
• Coalition on Abortion/Breast Cancer
• AbortionFacts.com – Breast Cancer
• CatholicCitizens.Org – The Scientific Debate That Never Happened
• ProInformation.net – Reaction to John Kindley's Wisconsin Law Review article