By Joel Brind, Ph.D.
Although you
wouldn't know it by media accounts, the published epidemiological evidence
overwhelmingly supports an abortion-breast cancer link (ABC link). For instance,
10 of 11 American studies and 24 of 30 worldwide have demonstrated the connection.
Faced with the evidence, most denials, if you will, go around the research.
They assert the claim that these studies' results are unreliable due to
a hypothetical entity referred to variously as "response bias,"
"reporting bias," or "recall bias."
We shall detail this alleged failure later in the article but the gist
of the argument is that the way certain categories of women report (or fail
to report) their abortions unfairly leaves the impression that women who've
aborted have a higher incidence of breast cancer.
Quietly and obliquely, in a letter to the editor published in this month's
issue of the British Medical Association's Journal of Epidemiology and
Community Health (JECH), the "evidence" almost universally
relied upon to back up this argument was abandoned by the very group which
first presented it! Let's look at the background.
In 1991, a Swedish team, including the prominent researcher Olav Meirik
of the World Health Organization, published the only paper to date which
claimed to show direct, statistically significant evidence of response bias.
Appearing in the American Journal of Epidemiology, the paper compared
data the team had gathered previously, by two different methods, on the
same population of Swedish women.
In papers appearing in the British publication Lancet and the British
Medical Journal in 1986 and 1990, respectively, the group published
combined data on Swedish and Norwegian women, data which were derived from
interviewing a patient group and a healthy group (the "controls")
about their reproductive history.
In 1989, the same group published a study in the British Medical Journal
based on computerized abortion registry records of the same Swedish women.
Such prospective records, i.e., records collected long before
anyone in the study got breast cancer, are by nature not subject to inaccuracies
due to recall which may occur in an interview-based, after-the-fact study
(retrospective).
According to the Swedish research team, the crux of the response bias argument
is this hypothesis: "a woman who had recently been given a diagnosis
of a malignant disease, contemplating causes of her illness, would remember
and report an abortion more consistently than would a healthy control"
(a woman without a malignant disease). The result would be an apparent but
misleading elevation in breast cancer risk since it would seem that breast
cancer patients have had more abortions than healthy women: response bias.
This seems plausible, but the evidence presented to back it up -- something
called "overreporting" -- is dubious indeed. A look at the data
tables in the 1991 paper reveals that seven Swedish breast cancer patients
reported having had an induced
abortion for which the computer had no record compared to only one healthy
(control) subject with no computer record.
To support their hypothesis, the authors assumed that the computer record
had to be right. Therefore, these eight women must have imagined abortions
that never really took place: they had "overreported" them!
Common sense to the contrary notwithstanding, this dubious assumption provided
the statistical significance for the otherwise insignificant finding of
"underreporting" by healthy women. It was good enough to rely
on by those bent on discrediting the ABC link.
Consider, for example, this wild exaggeration by Douglas Weed and Barnett
Kramer of the National Cancer Institute, in a December 1996 editorial in
the institute's own journal (JNCI). They wrote that the Swedish study
"show(ed) that healthy women consistently and widely underreport their
history of induced abortion."
Alternate interpretations of this "evidence" of response bias
went relatively unnoticed. For example, Janet Daling et al., in their
1994 abortion-breast cancer study published in the JNCI, expressed
a more logical view: "we believe it is reasonable to assume that virtually
no women who truly did not have an abortion would claim to have had one."
That brings us up to the present, and the current issue of the JECH,
where we now find Meirik et al. admitting that since the process
for obtaining a legal abortion in Sweden before 1975 was "time-consuming
and perceived by many as stigmatizing and paternalistic, [s]ome women therefore
had induced abortions abroad or unrecorded terminations of pregnancy."
They add, "We are not surprised to find some Swedish women confidentially
reporting having had induced abortions during the period 1966-1974 which
are not recorded (i.e., in the computerized registry) as legally induced
abortions."
This admission is as oblique as it is striking. The authors use the term
"overreporting" only once in the whole text of the letter, and
in quotes, as if the notion were someone else's and not theirs in the first
place. Even more peculiarly, having just acknowledged there is a lack of
any credible
justification, they reaffirm the idea of recall bias in the very next sentence!
The Meirik et al. letter was written as a criticism of the "Comprehensive
review and meta-analysis" of the ABC link which I had written with
co-authors from the Pennsylvania State University College of Medicine and
published in the October 1996 issue of the JECH. That gave us the
right to reply.
In our response, referring to the above admission by Meirik et al.,
we state: "This interpretation marks an about-face; an acknowledgement
that the computer registry may not be the 'gold standard' for assessing
the occurrence of induced abortion. Thus, based on discrepancies between
the interview and computer registry data, the claim of 'overreporting' is
acknowledged by Meirik et al. to be unfounded, and with that, significant
evidence of response bias evaporates."
However, this is only half the story, for in preparing our response to
the Meirik et al. letter, we had need to revisit this Swedish group's
earlier studies. In doing so, we uncovered evidence that rigorously proves
that they had ignored evidence of the ABC link in Norwegian women.
Specifically, the 1990 paper, which included data on induced abortion,
presented combined data for Swedish and Norwegian women. Since the
1991 paper compared interview-based data to computerized data only for the
Swedish women, it made it possible - - by subtracting data from the Swedish
women from the combined data for the Swedish and Norwegian women - - to
obtain separate data for the Norwegian subjects.
The result was startling: Though the Swedish breast cancer patients outnumbered
the Norwegian patients by more than 3 to 1 (317 to 105), only 26 of the
73 patients who reported having had an induced abortion were Swedish; 47
were Norwegian. In other words, of the 317 Swedish breast cancer patients,
about one in 12 (8.2%) had had an induced abortion, but almost one in
two (45%) of the Norwegian breast cancer patients had had an induced
abortion!
The effect of the wholly inappropriate statistical maneuver of combining
the Swedish and Norwegian data was to bury a definitely positive association
between induced abortion and breast cancer (i.e., increased risk) in Norwegian
women.
Numerically, we were able to prove that, in contrast to the 11% decreased
risk reported in the 1990 paper for the combined Swedish and Norwegian study
population, the data actually demonstrated an increased breast cancer risk
for Norwegian women somewhere between 12% and 123%. We were also able to
determine that, if both Swedish and Norwegian women in the study were affected
to the same extent by induced abortion, it would be just over 30% increased
risk the same 30% increased risk which we had calculated as a worldwide
average in our 1996 meta-analysis.
It remains to be seen just how much of an impact these revelations will
have on the shapers of public policy at the World Health Organization, the
National Cancer Institute, and other bodies who have bent over backwards
to find excuses to deny the reality of the ABC link. Now they have two fewer.
This article was adapted from an article appearing in the current issue of the Abortion-Breast Cancer Quarterly Update, which Dr. Brind publishes. Subscription information may be obtained by phone or fax at (914) 463-3728, by mail at P.O. Box 3127, Poughkeepsie, NY 12603, or from Dr. Brind's website: www.abortioncancer.com.