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Abortion - Breast Cancer link?

Medical studies of a possible ABC link

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Problems interpreting medical studies:

bulletCorrelation does not necessarily prove a cause and effect relationship: Medical studies are often designed to detect correlations of health factors. Unfortunately, a correlation between two factors does not necessarily imply that there is a cause and effect relationship between them. There might be a third factor involved. For example, some researchers suspect that the consumption of alcohol actually causes some breast cancers. A group of 1000 Mormon, Muslim, and/or Evangelical Christian women might well include a larger than average number of teetotalers, and a much lower number of abortions than average. A similar number of women with no particular religious affiliation might elect to have more abortions and to drink more alcohol. If both groups were combined in a study, a correlation between abortion and cancer would be found, even though there was no cause-and-effect linkage between abortion and cancer. The actual link would be between alcohol and breast cancer.
bullet"Case control studies" contain a major bias: Most of the early studies into an ABC link were of this type. Researchers interviewed a test group of women with breast cancer, asking them if they had had an abortion earlier in their life. A control group of healthy women were similarly interviewed.

"Women with breast cancer are more likely to tell the truth about past abortions because people with serious illnesses are motivated to report their medical history accurately to facilitate their treatment and recovery. But control groups of health people have less incentive to report honestly and, in fact, many women keep quiet about past abortions since it's a private and sensitive issue." 1

This factor is called "recall bias." It is a well-known effect. Other studies have shown that only 35 to 60% of actual abortions are reported in surveys.

It turns out that:

bulletMore women with breast cancer who have had an abortion, report it.
bulletMany, perhaps most, healthy women who have had an abortion suppress the information.

Case control studies are thus quite unreliable. However, they are often quoted by groups who want to "prove" an abortion-breast cancer link.

bullet"Historical Cohort Studies" are less biased: Such studies examine the complete "medical records for entire populations of women, over decades."  The researchers can determine how many women had abortions, how many developed breast cancer, how many had neither, and how many had both. Precise correlations can then be determined. It is important to realize that, for first trimester abortions, "No cohort study has shown evidence of an ABC link." 1

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Cohort studies of an ABC link:

bullet1997 Danish study: A massive cohort study was completed in Denmark and published in a peer-reviewed journal: the New England Journal of Medicine for 1997-JAN-9. 2 It finally laid the matter to rest for many cancer researchers. Every Danish woman born between 1935-APR-1 and 1987-MAR-31 was included in the study. That totaled about 1.5 million women. This study compares very favorably with many prior studies which only sampled one or two thousand. Dr. Mads Melbye and team from the Statens Serum Institute of Copenhagan found that no link generally exists between induced abortion and breast cancer. They did find a slightly increased risk of cancer among those few women who had a late-term abortion. But the numbers of women involved were so small that the results were not statistically significant. That is, they might have happened by chance. A future study involving even more women is required to resolve this question.

Dr. Patricia Hartge of the US National Cancer Institute prepared an editorial in the New England Journal of Medicine." She wrote that the Danish study

"...provides important new evidence to resolve a controversy that previous investigations have been unable to settle... a woman need not worry about the risk of breast cancer when facing the difficult decision of whether to terminate a pregnancy."

Dr. Joel Brind is publisher of ABC Quarterly Update, a magazine which promotes the ABC link. 3 He criticized the Danish study on a number of grounds. 4 The study authors responded with the statement: "We find [Brind's] argument self-contradictory and based on fundamental misconceptions about the cohort design."

bullet2001: A meta-analysis was reported in 2001-DEC by Tim Davidson. His article in Lancet Oncology reported that there was "insufficient data to justify warning women of future breast-cancer risk when counseling them about abortion."
bullet2004 world-wide meta-study: The Collaborative Group on Hormonal Factors in Breast Cancer in the UK reported the results of reanalysis of information from 53 epidemiological studies. Included were 83,000 women with breast cancer from 16 countries with liberal abortion laws. The study concluded that "Pregnancies that end as a spontaneous or induced abortion do not increase a woman’s risk of developing breast cancer." Commenting on the unreliability of data from case-control studies, they stated that:

"...studies of breast cancer with retrospective recording of induced abortion yielded misleading results, possibly because women who had developed breast cancer were, on average, more likely than other women to disclose previous induced abortions."

bullet2006 world-wide study: NARAL Pro-Choice America reports:

"A 2006 study published in the International Journal of Cancer examined the records of 267,361 women in nine countries and found no link between abortion and breast cancer, noting that 'the findings provide further unbiased evidence of the lack of an adverse effect of induced abortion on breast cancer risk'." 5,6,7

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Sponsored link:

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Other studies into a possible ABC link:

Miscarriages create the same hormonal disturbances as do induced abortions. One might expect that if a link were found between breast cancer and abortion, that a similar link would be also found between cancer and miscarriages. Yet, reliable studies have long shown that spontaneous miscarriages do not increase breast cancer rates.

Dozens of other studies have been made in an attempt to discover a correlation between abortion and the subsequent development of breast cancer. Some studies are inconclusive. Others show definitively that no linkage exists. Still others seem to identify such a link:
bulletOne conducted by the Fred Hutchinson Research Center in Seattle was published in the Journal of the National Cancer Institute. They studied 1,806 women and found a 50% increased risk of early breast cancer among women under 45 who had had induced abortions. 8
bulletAnother paper showed a massive increased risk of 370% among 1,000 African-American women over 50 years of age who had one or more induced abortions earlier in life. 9

Abortionfacts.com, a pro-life website, lists the results of many more studies that appear to have found a link between abortion and breast cancer. 10 They do not mention:

bulletThe many studies that have shown no linkage, or
bulletThat some of the studies that they quote are statistically inconclusive, or
bulletHistorical cohort studies, which are more reliable.

Those studies that show that an ABC link may exist all involved relatively small numbers of women. Their findings have not been considered conclusive by most physicians. Some studies which show a link have been criticized for internal statistical design flaws. One serious concern is the reliability of the data. As noted above, case control studies are inherently unreliable. When a test group of women with cancer is compared to a control sample of women without cancer, the former may be more likely to volunteer the information that they had undergone an abortion. One report stated that:

"In addition, those women reporting induced abortions had less favorable risk profiles (parity, age at first term pregnancy, and lactation) than women reporting spontaneous abortions." 11

One source states that "Montana and Mississippi already require that women seeking an abortion be informed that the procedure could increase their risk of developing breast cancer." 9

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References used:

The following information sources were used to prepare and update the above essay. The hyperlinks are not necessarily still active today.

  1. Joyce Arthur, "Abortion and Breast Cancer: A forged link," The Humanist, 2002-MAR/APR, Pages 7 to 9.
  2. Dr. Mads Melbye et al, New England Journal of Medicine, 1996-JAN-8
  3. Dr. Joel Brind, "Abortion-breast cancer link," at: http://www.abortioncancer.com/ 
  4. Dr. Joel Brind, "Rotten in Denmark," at: http://www.abortioncancer.com/ 
  5. "The safety of legal abortion and the hazards of illegal abortion," NARAL, at: http://www.prochoiceamerica.org/
  6. "Breast cancer risk in relation to abortion: Results from the EPIC study," 119 International Journal of Cancer, 1741-45 (2006).
  7. "Abortion seen not related to breast cancer risk," REUTERS, 2006-OCT-16.
  8. Dr. Janet Daling et al, Journal of the National Cancer Institute, 1994-NOV-2
  9. Article, Journal of the National Medical Association, 1993-DEC.
  10. Dr. & Mrs. J.C. Willke, "Why can't we love them both," at: http://www.abortionfacts.com/
  11. "Induced abortion and breast cancer: the scientific evidence," Medical Sciences Bulletin, at: http://pharminfo.com/
  12. Margaret Woodbury, "Judge to rule on abortion, breast cancer link," 2002-FEB-17, at: http://www.womensenews.org/

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Copyright 1998 to 2007 by Ontario Consultants on Religious Tolerance
Latest update: 2007-MAY-24
Author: B.A. Robinson

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