Abortion and breast cancer: a forged link

Humanist, March-April, 2002 by Joyce Arthur

There simply is no known mechanism that would cause the alleged ABC link. Brind speculates that abortion suddenly interrupts the estrogen surge, leaving rapidly growing breast cells in an undifferentiated state and more vulnerable to carcinogens. However, this hypothesis has no empirical support. Besides, how would one then explain the fact that studies show no link between miscarriage and breast cancer, as anti-abortionists acknowledge? Brind claims the "raging-hormones-cut-short" problem doesn't affect miscarriage, since most miscarriages are caused by a lack of pregnancy hormones. Not so--the majority of miscarriages are actually caused by genetic defects in the egg/embryo, and other causes; only an estimated 10 percent or so of miscarriages are caused by hormonal deficiencies. This means there is probably no significant difference between the effects of miscarriage and abortion--so if miscarriage doesn't lead to an increased risk of breast cancer, then, of course, neither would abortion.

For the sake of argument, let's suppose that Brind's ABC link is real. What would it really mean? He claims that abortion may boost the risk of breast cancer by 30 percent, but this increase is not really that significant. For example, the risk is 200 percent to 300 percent higher for a woman whose mother or sister had breast cancer alter age fifty. Even this well-established risk factor is considered moderate by scientists. In comparison, the alleged ABC link barely qualifies; even if it's real, the risk is close to negligible. To put it another way, the National Cancer Institute estimates the current risk of breast cancer to be one in 2,525 for a woman in her thirties; if that risk were increased by 30 percent, it would mean one in 1,942 women would get breast cancer.

Second, correlation doesn't equal causation, which means some other factor could be responsible for any increased breast cancer risk, thus confounding the study results. For example, women with a first full-term pregnancy after age thirty face a breast cancer risk two to three times higher than women with a full-term pregnancy before age twenty. If a study included many women who had aborted their first pregnancy when they were young, effectively postponing motherhood, we might find a correlation between abortion and breast cancer, but delayed childbearing would be the more probable cause of the increased risk.

Anti-abortion "researchers" are notorious for confusing correlation with causation, which is showcased by a new study, privately funded by a British anti-abortion group. The "study"--published by lone author Patrick Carroll and not peer reviewed--blames thirty years of legalized abortion for rising rates of breast cancer in some countries. Dismissed or ignored are many other probable causes that have also proliferated in the last thirty years--including delayed childbearing, smaller family size, better cancer-screening methods, environmental contaminants, obesity in mid-life, and the use of oral contraceptives and hormone replacement therapy.