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.

In 1994, a paper in the Journal of the National Cancer Institute drew the public’s attention—and fire.  After interviewing 845 women who had a breast cancer diagnosis at age 45 or younger, as well as 961 “control” subjects, researchers led by Janet Daling of Seattle’s Fred Hutchinson Cancer Center observed a 50 percent higher risk of breast cancer among women who admitted to having had an abortion. (The association didn’t hold for women who said they’d had a miscarriage.) Anti-abortion groups like the National Right to Life trumpeted the report. In an accompanying editorial, epidemiologist Lynn Rosenberg acknowledged the relevance of “reproductive factors” in breast cancer development, but faulted the study’s reliance on personal, emotionally charged interviews.

The debate moved from women’s health to the political realm. Some on the left, such as Michael Castleman in Mother Jones, posited that pro-abortion rights interests risked credibility by ignoring data. The Economist countered this line of thinking with an article on “Abortion, breast cancer and the misuse of epidemiology.” Fear played in all too readily. Sociologist Barry Glassner recalls bus banner ads in Baltimore proclaiming, "Women who choose abortion suffer more and deadlier breast cancer."

What might have settled the question was a 1997 New England Journal of Medicine report. This gigantic analysis of more than 1.5 million Danish women didn’t involve interviews. The investigators culled data from Denmark’s Civil Registration System, Cancer Registry, and mandatory abortion records. They found no correlation, period. More than a few women, Jane Brody in the New York Times among them, expressed relief and hope that the study’s comprehensive scope and reliable data might “put to rest a longstanding concern.”

It didn’t. Controversy persisted to such a degree that in July 2002, the National Cancer Institute  responded to a nudge from congressional conservatives by changing information on its website. Pro-abortion rights lawmakers charged the agency with distorting and suppressing scientific information for ideological reasons. After some back-and-forth and a congressional investigation, the institute convened geneticists, epidemiologists, oncologists, and other experts to review all evidence. The conclusion rests on an NCI fact sheet: Elective abortions are not associated with an increased risk of breast cancer.

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The ethical principle of informed consent means this: A patient should know, and understand as best possible, the likely risks and benefits of a medical procedure before signing on. Now, at least five states sponsor misleading, partisan-promoted material on abortion and breast cancer risk.

Around the country, new choice-cramping laws are in the works. Many of the proposed informational mandates exploit the concept of informed consent to assure its opposite: promulgation of untruths about abortion. These bills appeal, falsely, to reason—with smart-sounding, progressive-seeming phrases, like “a right to know.” They feed  on women’s fear of a dreaded disease. Few pregnant women are sufficiently versed in science or statistics to refute their lawmakers’ misconceptions.

The bottom line is that most breast cancer cases go unexplained. There are infinite variables in an ordinary woman’s life. If I were to counsel a woman contemplating an abortion, that’s what I’d say. We know too little.

Elaine Schattner is a trained oncologist who lives and teaches medicine in New York City. She blogs at Medical Lessons.

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