Rusty Link: The Lackluster Science Behind the Abortion–Breast Cancer Connection 

Health and medicine explained.
May 23 2012 6:16 AM

Do Abortions Cause Breast Cancer?

The shaky science behind Kansas’ House Abortion Act.

There is no link
There is no link

Photograph by iStockphoto.

In Kansas, legislators recently passed the No Taxpayer Funding for Abortion Act. If enacted into law, the bill would require doctors to tell pregnant women of a relationship between abortion and breast cancer. This news follows passage by the New Hampshire State House of the Women’s Right To Know Act Regarding Abortion Information. These related laws are unlikely to gain approval by the state senates. But there’s a trend: A similar measure took effect in Texas in February. Now, providers there must inform pregnant women about “the possibility of increased risk of breast cancer following an induced abortion,” the so-called ABC link.

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In the decade following Roe v. Wade, the occurrence of breast tumors in the United States soared. The coincidental rise in case numbers with legalized abortions led some to speculate that terminating a pregnancy might boost a woman’s odds. The link is plausible because female hormones and fertility influence mammary growth and tumors. After a spate of conflicting reports in the 1980s and ’90s, a consensus emerged that there’s no meaningful tie. Rather, modern demographics—like birth control use, delayed childbirth, and obesity—combined with increased detection by mammography, overwhelmingly account for the rise in breast cancer diagnoses. The most recent edition of Principles and Practice of Oncology, the “bible” of cancer medicine, does not list abortion as a risk factor. Still, anti-abortion groups press the association.

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What’s curious from a med-ethics standpoint is the way in which anti-abortion activists have adopted the language of patient empowerment, like a Woman’s Right To Know, and turned it upside down. The nascent laws insist that those contemplating the procedure be made aware of a falsehood or, at best, an unproved and frightening correlation. They stipulate confusion rather than informed consent.

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Few doubt that a woman’s reproductive history influences her chances of getting breast cancer. As early as 1703, Italian physician Bernardino Ramazzini reported that nuns suffered breast tumors with relative frequency. A century ago, the British Ministry of Health commissioned Dr. Janet Clay-Laypon to examine possible roots of the malignancy. In then-innovative case-control studies, Clay-Laypon surveyed 508 breast cancer patients at English and Scottish hospitals. For controls, she questioned women with other medical conditions. Her 1926 monograph, A Further Report on Cancer of the Breast, confirmed what doctors had long suspected: Women who deliver few children and marry late are more likely to develop the disease.

Today, what’s known about breast cancer causes remains slim. Only a small fraction of cases trace to genetics. Having your first period at an early age or going through menopause late correlates with increased risk. Bearing multiple kids and breast-feeding may lower your risk. Hormonal birth control and replacement “therapy” after menopause are implicated too, as is radiation exposure—whether from bombs, treatment of another cancer, or too many CT scans. Environmental toxins, broadly, and a few specific chemicals are named culprits, though few are incontrovertible. Other factors, (like not exercising, drinking alcohol, or being fat for older women) might increase one’s chances. But essentially all the science is correlative. Absolute proof is absent.

The notion of an abortion/breast cancer link gained traction around 1981. A group of Southern California investigators observed an apparent 2.4-fold increase in breast cancer among young women who said they’d had either a miscarriage or an elective abortion in the first trimester of pregnancy. Their British Journal of Cancer report was limited and unusual: It included just 163 patients, all with cancer diagnoses by age 32. And the researchers’ methodology was telling. They asked the women if they’d used oral contraceptives, and how many times they’d been pregnant, delivered, miscarried, or had abortions. For “controls” the investigators approached the patients’ old high school friends and neighbors—literally, by going house to house on the blocks where they lived—and posed to them the same personal questions.

Between 1980 and 1997, scientists produced dozens of reports on the putative ABC link, finding one side or the other in rough tandem with political outbursts over abortion rights. Clinicians, evidently, were oblivious: In a study of California physicians’ attitudes about breast cancer, none mentioned abortion among 29 possible causes.

The overriding problem is that abortion’s a loaded subject. Same goes for breast cancer. Recall bias weighs heavily in case-control studies on topics like these, limiting or abrogating their value. It’s not unusual for breast cancer patients to feel ashamed of their illness. Some pore over the details of their moral and physical past selves, wondering what they’ve done to cause the ailment. Even if they don’t feel guilty, patients may think that knowing they’ve had an abortion could make a difference in doctors’ understanding of their medical condition. By contrast, a person not undergoing breast cancer treatment has little reason to tell a stranger she once decided to terminate a pregnancy.