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. In early
pregnancy the level of
estrogens increase and initiates
breast growth in preparation for
lactation. The abortion-breast cancer 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. The hypothesis, however, has not been verified and abortion is not considered an actual breast cancer risk by any major cancer organization.
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.
[Melbye M. et al. (1997) Induced abortion and the risk of breast cancer. (abstract) New England Journal of Medicine, 336, 81-5. Retrieved 2006-01-11 from PubMed.] 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."
[National Cancer Institute. (2003-03-04). Summary Report: Early Reproductive Events and Breast Cancer Workshop. Retrieved 2006-01-11.] 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."
[Beral V. et al. (2004) Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83,000 women with breast cancer from 16 countries. (abstract) The Lancet, 363, 1007-16. Retrieved 2006-04-12 from PubMed.]Of over 100 experts at the National Cancer Institute workshop,
Dr. Joel Brind, abortion-breast cancer's primary advocate and an invitee to the workshop, filed the only dissenting opinion which criticized the NCI and Melbye conclusions.
[Brind, Joel. (2003-03-10). Early Reproductive Events and Breast Cancer: A Minority Report. Retrieved 2006-03-24.] Brind points out the majority of interview-based studies have indicated a link, and some have been demonstrated to be
statistically significant,
[Etters.net – American abortion-breast cancer studies] but there remains debate as to their reliability because of possible
response bias. Most medical professionals agree with the recent research that concludes no abortion-breast cancer association,
[American Cancer Society. (2006-10-03) Cancer.org â€" What Are the Risk Factors for Breast Cancer? Retrieved 2006-03-30.] and the ABC issue is seen by some as merely a part of the current
pro-life "women-centered" strategy against abortion.
[Arthur, Joyce. (2002) ProChoiceActionNetwork-Canada.org â€" Abortion and Breast Cancer â€" A Forged Link] Nevertheless, gaps and inconsistencies remain in the research, and the subject continues to be one of mostly political but some scientific contention.
[Jasen, P. (2005) Breast Cancer and the Politics of Abortion in the United States. Medical History 2005 October 1; 49(4): 423â€"444.]The National Cancer Institute (NCI) conducted a workshop to evaluate the scientific evidence regarding the abortion-breast cancer hypothesis. This was done in response to alterations to the NCI website by the
Bush administration in November 2002.
[democrats.reform.house.gov – Breast Cancer Risks] The workshop concluded that the evidence was well established against an abortion increasing a woman's risk of breast cancer.
It has been reported the workshop largely used Dr. Melbye's 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."
[catholiccitizens.org – Abortion and Breast Cancer: The Scientific Debate That Never Happened] 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.
[bcpinstitute.org – FACT SHEET… Re: Review of Abortion-Breast Cancer link (ABC link) at National Cancer Institute (NCI) workshop on "Early Reproductive Events and Breast Cancer Risk", held Feb 24-26, 2003] The main expert who made the formal abortion-breast cancer presentation, Dr. Leslie Bernstein, primarily had expertise in obesity and
exercise in relation to breast cancer. Dr. Daling, who has published on the abortion-breast cancer 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.
[Melbye M. et al. (1999) PubMed Preterm delivery and risk of breast cancer. Br J Cancer. 1999 May;80(3-4):609-13.] No minority or dissenting report was requested but Dr. Brind did file a dissenting opinion.
[Cancer.gov – Minority Dissenting Comment Regarding Early Reproductive Events and Breast Cancer Workshop]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,
[Brody, Jane E. (1997) JunkScience.com â€" Breast Cancer Awareness May Carry Its Own Risks] there exists the concern that pro-lifers use it as a scare tactic. Abortion-breast cancer 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.
At the same time pro-life organizations lobby to increase obstacles to abortion, such as mandated
counseling, waiting periods, and parental notification,
[Guttmacher.org – Facts on Induced Abortion in the United States] and some feel that pro-life advocates 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.
[Frontline: 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 research on abortion-breast cancer (ABC) has used including testing of
rats,
interviews (
case-
control),
meta-analysis and
cohorts. ABC studies have been conducted since
1957,
but this article covers relevant recent ABC research history referenced in the ABC debate, 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% followed by 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.
adds further complications since an uncorroborated study has indicated it is associated with a history of induced abortion
[Moreau C. et al. (2005) PubMed Previous induced abortions and the risk of very preterm delivery: results of the EPIPAGE study. BJOG. 2005 Apr;112(4):430-7.] and higher breast cancer risk.
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. Hormones being a key factor for cancer risk is well established. Steroidal
estrogen was added to the
federal carcinogen list in December 2002. The
American Cancer Society (ACS)
[Cancer.org – Breast Cancer Facts & Figures 2001-2002.] and the
National Cancer Institute (NCI)
[Cancer.gov – Estrogen and Cancer] note reproductive hormones can elevate breast cancer risk.
[ScienceDaily.com – New Federal Report On Carcinogens Lists Estrogen Therapy, Ultraviolet, Wood Dust] In particular a
Women's Health Initiative HRT study cut short from an elevated breast cancer risk using estrogen with
progestin.
[jama.ama-assn.org – Influence of Estrogen Plus Progestin on Breast Cancer and Mammography in Healthy Postmenopausal Women]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.
[Feuer E.J. et al. (1993) PubMed The lifetime risk of developing breast cancer. Natl Cancer Inst. 1993 Jun 2;85(11):892-7.] 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
MelbyeA large, highly regarded ABC study was published by Dr. Melbye et al. (1997) 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.
[Osler M. et al. (1990) PubMed Family planning services delivery. Danish experience. Dan Med Bull. 1990 Feb;37(1):95-105.] 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
oral contraceptives 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 oral contraceptives 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." 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, there is no contradiction.
[AbortionBreastCancer.com â€" ABC in the courts: Dramatic ABC testimonyin Florida's parental notification appeal]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).
HoweThe 1989 study 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).
[Howe HL. et al. (1989) PubMed Early abortion and breast cancer risk among women under age 40. Int J Epidemiol. 1989 Jun;18(2):300-4.] 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.
Dr. Newcomb and Michels pointed out it examined only very young women and did not account for some confounding factors such as family history of breast cancer.
[Woodbury MA. (2002) Womensenews.org â€" Judge to Rule on Abortion, Breast Cancer Link] However, 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 the
Britain-based International Journal of Epidemiology published it in 1989.
[Frezza, Steve. (1993)web.archive.org â€" The Link Between Abortion & Breast Cancer.]Lindefors-HarrisAnother cohort study by Dr. Lindefors-Harris et al. (1989) was done looking at 49,000 women who had received abortions before the age of 30 in Sweden (65 breast cancer cases â€" compared with estimate of occurrence in general population).
[Harris BM. et al. (1989) PubMed Risk of cancer of the breast after legal abortion during first trimester: a Swedish register study. BMJ. 1989 Dec 9;299(6713):1430-2.] 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.
Meta-analysis
BeralIn March 2004, Dr. Beral et al. published a study in
The Lancet as a collaborative reanalysis on
Breast cancer and abortion.
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.
[bcpinstitute.org – FACT SHEET…Abortion and Breast Cancer: re: "collaborative reanalysis of data" published in Lancet 3/25/04 (1)]BrindA meta-analysis was conducted by Dr. Brind et al. (1996) with both pro-choice and pro-life scientists that examined 28 published studies.
[Brind, J. et al. (1996) PubMed – Induced abortion as an independent risk factor for breast cancer: a comprehensive review and meta-analysis. J Epidemiol Community Health. 1996 Oct;50(5):481-96.] 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.
[PlannedParenthood.org – Anti-Choice Claims About Abortion and Breast Cancer] 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."
[nelh.nhs.uk – The Care of Women Requesting Induced Abortion]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.
[Robinson, B.A. (2006) ReligiousTolerance.org â€" IS THERE A LINK BETWEEN ABORTION AND BREAST CANCER?] Here are a few interview studies of note.
DalingDr. 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.
[Daling J.R. et al. (1994) PubMed Risk of breast cancer among young women: relationship to induced abortion. J Natl Cancer Inst. 1994 Nov 2;86(21):1584-92.] 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).
[Daling J.R. et al. (1996) PubMed Risk of breast cancer among white women following induced abortion. Am J Epidemiol. 1996 Aug 15;144(4):373-80.] 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 noted that patients with cervical cancer may report differently than breast cancer patients.
[Rookus M.A. (1996) PubMed Induced abortion and risk for breast cancer: reporting (recall) bias in a Dutch case-control study. J Natl Cancer Inst. 1996 Dec 4;88(23):1759-64.]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."
SandersonA 2001 study 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.
[Sanderson M. (2001) PubMed Abortion history and breast cancer risk: results from the Shanghai Breast Cancer Study. Int J Cancer. 2001 Jun 15;92(6):899-905.] Since induced abortion is common, legal, and even mandated by the government in China, the recall bias was minimized.
[PlannedParenthood.org â€" Anti-Choice Claims About Abortion and Breast Cancer]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.
[Malec, K. (2003) CatholicCitizens.org â€" Abortion Breast Cancer Coalition Reveals Health Magazine Cooperating in Government Cover-up, Falsely Reassures Women of the Safety of Abortion.][Brind J. (2004) PubMed Breast cancer and induced abortions in China. Br J Cancer. 2004 Jun 1;90(11):2244-5; author reply 2245-6.] 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.
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 for ABC normally 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 Dr. Bartholomew in 1998. It concluded that if studies least susceptible to response bias are considered, they suggest there is no ABC link.
[Bartholomew L.L., Grimes D.A. (1998) PubMed The alleged association between induced abortion and risk of breast cancer: biology or bias? Obstet Gynecol Surv. 1998 Nov;53(11):708-14.] 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."
[Weed D.L., Kramer B.S. (1996)PubMed Induced abortion, bias, and breast cancer: why epidemiology hasn't reached its limit. J Natl Cancer Inst. 1996 Dec 4;88(23):1698-700.] This not only commented on the patients in studies, but focused its attention on the potential biases of the researchers themselves.
Lindefors-HarrisThe Lindefors-Harris (1991) study was the first major study to examine response and recall bias.
[Lindefors-Harris B.M. et al. (1991) PubMed Response bias in a case-control study: analysis utilizing comparative data concerning legal abortions from two independent Swedish studies. Am J Epidemiol. 1991 Nov 1;134(9):1003-8.] 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,"
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.
[Meirik O. et al. (1986) PubMed Oral contraceptive use and breast cancer in young women. A joint national case-control study in Sweden and Norway. Lancet. 1986 Sep 20;2(8508):650-4.] These women were interviewed as mothers, which could have increased the tendency to underreport, given that a mother might not want to appear unfit.
Subsequently the Lindefors-Harris obliquely retracted the 50% conclusion in 1998,
[Meirik, O. et al. (1998) jech.bmjjournals.com (PDF) â€" Relation between induced abortion and breast cancer. J Epidemiol Community Health 1998;52:209â€"212] but reasserted since the
Denmark (Melbye 1997) cohort study,
found no link the 30% increased risk in the Brind meta-analysis
must be the accumulative result of response bias.
RookusThe Rookus (1996) study 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 that it was attained with an extremely small sample size.
[Brind J. (1997) PubMed Re: Induced abortion and risk for breast cancer: reporting (recall) bias in a Dutch case-control study. J Natl Cancer Inst. 1997 Apr 16;89(8):588-90.] (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 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 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.
[Russo J., Russo I.H. (1980) PubMed Susceptibility of the mammary gland to carcinogenesis. II. Pregnancy interruption as a risk factor in tumor incidence. Am J Pathol. 1980 Aug;100(2):497-512.] A more thorough examination of the phenomenon was conducted in 1982, which confirmed the results.
[Russo J. et al. (1982) PubMed Differentiation of the mammary gland and susceptibility to carcinogenesis. Breast Cancer Res Treat. 1982;2(1):5-73.] A later study in 1987 further explained their previous findings.
[Russo J., Russo I.H. (1987) PubMed Biological and molecular bases of mammary carcinogenesis. Lab Invest. 1987 Aug;57(2):112-37.] 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.
[AnnieAppleseedProject.org â€" Adolescent Diet & Risk of Bca]In a
Discover article sidebar 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.
[Yeoman, Barry. (2003) BarryYeoman.com â€" The Scientist Who Hated Abortion. Discover.]Spontaneous abortion
Studies of spontaneous abortions (
miscarriages) have generally shown no increase in breast cancer risk,
[Brewster D.H. et al. (2005) PubMed Risk of breast cancer after miscarriage or induced abortion: a Scottish record linkage case-control study. J Epidemiol Community Health. 2005 Apr;59(4):283-7.] although a study by Dr. Paoletti concluded there is a "suggestion of increased risk" 1.2 (0.92 to 1.56) after 3 or more pregnancy losses.
[Paoletti X., Clavel-Chapelon F. (2003) PubMed Induced and spontaneous abortion and breast cancer risk: results from the E3N cohort study. Int J Cancer. 2003 Aug 20;106(2):270-6.] 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.
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 spontaneous abortion is not analogous to an induced abortion. While it is true most miscarriages are not
caused by low hormones, most miscarriages are
characterized by low hormone levels.
[web.archive.org st-marys.nhs.uk â€" What causes recurrent miscarriage?] One of the first studies on hormone levels and spontaneous abortion by Kunz & Keller (1976) showed that when
progesterone is abnormally low a miscarriage occurs 89% percent of the time.
[Kunz J., Keller P.J. (1976) PubMed HCG, HPL, oestradiol, progesterone and AFP in serum in patients with threatened abortion. Br J Obstet Gynaecol. 1976 Aug;83(8):640-4.] This is also reflected in studies published by Hertz et al. (1979)
[Hertz J.B. et al. (1979) PubMed Estradiol, estriol and human placental lactogen in serum in threatened abortion. Acta Obstet Gynecol Scand. 1979;58(4):365-70.] and in more detail by Stewart et al. (1993).
[Stewart D.R. et al. (1993) jcem.endojournals.org (PDF) Enhanced Ovarian Steroid Secretion before Implantation in Early Human Pregnancy. J Clin EndocrinolMetab 76: 1470-1476, 1993.]A distinction should also be made for second trimester miscarriages as their hormonal characteristics differ from first trimester miscarriages.
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."
[Robinson B.A. (2004) ReligiousTolerance.org â€" ABORTION AND BREAST CANCER LINK? VERBAL AND LEGAL ATTACKS BY PRO-LIFE GROUPS] (emphasis in original)
The case was originally scheduled for
September 11, 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.
[Lynne, Diana. (2002) WorldnetDaily.com â€" Judge rules in favor of abortion clinic] 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."
[CRLP.org â€" Judge Rejects Abortion-Breast Cancer Scare Tactic] 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."
[Thaney, Jennifer. (2002) WomensPress.com â€" Controversy over alleged breast cancer link lands abortion clinic in court] Kindley also wrote an article published in 1998 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.
[Kindley, John. (1998) JohnKindley.com â€" Wisconsin Law Review]The decision was appealed and on
September 23, 2003 to the
North Dakota Supreme Court which ruled the false advertising law
[legis.nd.gov (PDF) â€" False Advertising] 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."
[caselaw.lp.findlaw.com â€" Amy Jo Kjolsrud v. MKB Management Corporation] 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.'"
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.
[Meckler, Laura. (2004) Boston.com â€" Questions on states' abortion warnings] These state laws put up further barriers to elective abortion,
[Yeoman, Barry. (2001) MotherJones.com â€" The Quiet War on Abortion] 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 from women who might contend they should have been told of the ABC link possibility prior to having an abortion.
[Merz, Jon F. (2002) PierceLaw.edu â€" An Empirical Analysis of the Medical Informed Consent Doctorine: Search for a "Standard" of Disclosure]A vocal pro-life minority insist there is an abortion-breast cancer link, but no major international cancer organization considers abortion to be a breast cancer risk. The scientific consensus is that the evidence is inconclusive.
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 abortion-breast cancer 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.
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
