Abortion - Breast Cancer link?
Medical studies of a possible ABC link
Problems interpreting medical studies:
||Correlation 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.
||"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
"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:
||More women with breast cancer who have had an abortion, report it.
||Many, perhaps most, healthy women who have had an abortion suppress the
Case control studies are thus quite unreliable. However, they
are often quoted by groups who want to "prove" an abortion-breast cancer link.
||"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
Cohort studies of an ABC link:
||1997 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
"...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."
||2001: 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."
||2004 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."
||2006 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
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
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:
||One 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
||Another 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:
||The many studies that
have shown no linkage, or
||That some of the studies that they quote are statistically inconclusive, or
||Historical 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
The following information sources were used to prepare and update the above
essay. The hyperlinks are not necessarily still active today.
- Joyce Arthur, "Abortion and Breast Cancer: A forged link," The
Humanist, 2002-MAR/APR, Pages 7 to 9.
- Dr. Mads Melbye et al, New England Journal of Medicine, 1996-JAN-8
Dr. Joel Brind, "Abortion-breast cancer link," at:
Dr. Joel Brind, "Rotten in Denmark," at:
"The safety of legal abortion and the hazards of illegal abortion," NARAL,
- "Breast cancer risk in relation to abortion: Results from the EPIC study,"
119 International Journal of Cancer, 1741-45 (2006).
- "Abortion seen not related to breast cancer risk," REUTERS, 2006-OCT-16.
- Dr. Janet Daling et al, Journal of the National Cancer Institute,
- Article, Journal of the National Medical Association, 1993-DEC.
Dr. & Mrs. J.C. Willke, "Why can't we love them both," at:
"Induced abortion and breast cancer: the scientific evidence,"
Medical Sciences Bulletin, at:
Margaret Woodbury, "Judge to rule on abortion, breast cancer link,"
Copyright 1998 to 2007 by Ontario
Consultants on Religious Tolerance
Latest update: 2007-MAY-24
Author: B.A. Robinson