Abortion may seem an unlikely trigger for breast tumors, but it’s a plausible one. During puberty, and again during the first trimester of pregnancy, high estrogen levels cause a woman’s breast cells to multiply rapidly. The new cells remain unformed and somewhat cancer-prone until the later stages of pregnancy. But as other hormones ready the cells to make milk, they become more resistant to malignancy. It’s well known that giving birth reduces a woman’s long-term breast-cancer risk, and logic suggests that interrupting a pregnancy might have the opposite effect.
Confirming that hunch has been a dicey enterprise, both scientifically and politically. When studies have suggested a statistical link between abortion and breast cancer, anti-abortion activists have rushed to exaggerate the implications. Scientists and journalists have rushed just as fast to dismiss positive findings by fixating on any possible flaw in the research methods. To cut through the fog, Brind and his colleagues compiled 23 studies involving women who had undergone induced abortions (spontaneous miscarriages generally occur too early in pregnancy to have much effect on breast cells). Eighteen of the 23 showed a significant association between abortion and breast cancer, as did five of the six published after the analysis was underway. ““The consistency is remarkable,’’ says Brind, an endocrinologist at New York City’s Baruch College. ““The same pattern shows up among white women, black women and Asian women, regardless of diet or lifestyle.''
By pooling results from the studies, Penn State University statistician Vernon Chinchilli calculated that women who had been through an abortion had a breast-cancer ““odds ratio’’ of 1.3, meaning their risk rose by 30 percent. Statistically, that’s not much; other factors, such as a family history of breast cancer, can push a woman’s odds ratio to 3 or 4. But even a slight increase in risk can have large consequences. In the United States, where an average woman already faces a 12 percent risk of developing breast cancer by the age of 90, having an abortion could push the chances to 16 percent. And given that 800,000 American women have first-time abortions each year, the odds suggest that 25,000 of them could develop tumors as a result. That’s hardly an argument for banning abortion. Studies suggest that one drink a day may carry a similar risk, and no one is calling for prohibition. But if women have a right to choose abortion, they surely have a right to know the risks.
