“The abortion-breast cancer link (ABC link): Those stubborn facts again! Part One

By Joel Brind, Ph.D.

Joel Brind, Ph.D.

The resurgence of the abortion-breast cancer debate—this time prompted by the introduction of bills in three states that would require warning women seeking abortion about the link between induced abortion and breast cancer—has again generated vicious and dishonest denials that any link exists. The worst example—but only one of many—was produced by Eric Zorn, writing in the Chicago Tribune.

In the face of Zorn’s malicious invective (he calls proposed “women’s right to know” acts now pending in New Hampshire, Kansas, and New Jersey “Activists’ Right to Lie to Women” acts), it’s a good time to set the record straight with accurate, scientific facts.

In this first of three articles on the ABC link, I’ll chronicle the history of epidemiological data going back over 50 years that shows a consistent statistical connection between a history of induced abortion and a higher incidence of breast cancer among women all over the world. I’ll also briefly talk about the curious logic used by deniers of the ABC link.

By way of background, abortion raises a woman’s risk for breast cancer in two ways; the debate is over the second, not the first. Scientists have long understood that the risk of breast cancer is reduced when a woman completes a full-term pregnancy. This “protective effect of childbearing” is lost with an abortion. The second way abortion increases the likelihood of breast cancer is that an abortion leaves a woman with more cancer-vulnerable breast tissue than she had before she became pregnant.

In 1957, a nation-wide study in Japan published in  the Japanese Journal of Cancer Research found that women who had breast cancer reported having had three times as many pregnancies end with an induced abortion. Of course, there were few studies in those days, as induced abortion was neither legal nor common in most of the world—and breast cancer was not that common either!

Most studies, in fact, did not distinguish between induced abortion and spontaneous abortion (what we usually refer to as miscarriage), a natural event that generally does not increase the risk of breast cancer. I will talk about the importance of this distinction in Parts Two and Three,

Then there were the results of a very prominent series of World Health Organization-sponsored studies in the late 1960’s. Led by a Harvard research team, the WHO study looked at women from four continents to find out whether early pregnancy reduces breast cancer risk. That turned out to be true for full-term pregnancies. But they also found that the results “were in the direction which suggested increased risk associated with  abortion — contrary  to  the reduction in risk associated with full-term births.”

The famous 1970 paper that summarized these WHO findings firmly established that full-term pregnancies confer protection against breast cancer. It has been unequivocal for over 40 years that a pregnant woman who chooses abortion will end up with a higher long-term risk of breast cancer than if she chooses instead to let nature take its course.

Every reasonable standard of informed consent requires a doctor to warn a patient of any adverse health consequences of having the intervention in question—abortion in this case—compared to not having the intervention. That alone defines a duty for abortion practitioners to inform their patients of the increase in future breast cancer risk.

But the ensuing four decades of research around the world, a world with an ever increasing number of women having had an induced abortion, have shown that it is even worse: Women who choose abortion are more likely to get breast cancer than if they had not gotten pregnant in the first place.

This trend, known among epidemiologists as the “independent risk” of abortion, has been the center of the controversy raging in the public square. Evidence of this independent risk of abortion first showed up among American women in a prominent study from USC published in 1981 in the British Journal of Cancer. Another dozen American studies showed the independent effect during the 1980’s and 90’s, as well as another dozen studies from Europe and Asia.

In 1996, along with colleagues from the Penn State Medical College, I published, in the British Medical Association’s epidemiology journal, a meta-analysis of all 23 studies then extant. Our paper proved that the average 30% increase in breast cancer risk among women who have had an induced abortion was “statistically significant”: in other words, this increase was more than 95% certain not to be due to chance. In the last five years, studies continue to emerge from nations where both abortion and breast cancer used to be rare–China, Iran, Turkey, Armenia—showing a clear and significant independent ABC link.

Yet strangely—and tragically—to all the world’s most prominent purveyors of public health information, from the U.S. National Cancer Institute, American Medical Association and the cancer charities such as the American Cancer Society and Komen, to Health Ministries around the world and the WHO itself, the ABC link does not exist!

And the argument upon which all the denials are based boils down to something called variously, “reporting bias” or “response bias.” It goes like this.

When a study population of women is interviewed to determine their reproductive history, the argument is that healthy women will be more reluctant to admit they had an abortion, whereas women with cancer are more likely to tell the truth about their abortion history.

If this is true, then studies which rely on interviews that look back in time (retrospective studies) will overestimate the association of induced abortion with breast cancer patients, compared to healthy women. Proponents of this hypothesis go on to claim that only a study based on medical records, or one which follows women prospectively in time– i.e., a study in which the abortions are recorded before anybody knows who will get breast cancer–can give accurate results.

As much of a stretch as the response bias hypothesis seems–flying in the face of a half-century’s worth of data from studies on women from all over the world conducted by long-standardized epidemiological methods–it is a testable hypothesis. In fact it has been tested again and again, and found wanting, but that has not muted the chorus of official denial of the ABC link.

That leads to part II of this series, in which we will segue from the ABC link as the focus of our inquiry, to the world-wide cover-up of the ABC link, and its now over 40-year-long trail of published evidence.

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