An abortion or a miscarriage does not increase a woman’s risk of breast cancer, according to results released Monday from a decadelong study of more than 100,000 women.
The findings are the latest, and perhaps most convincing, in a series of studies that have discredited a concern used by anti-abortion activists to dissuade women from having the procedure.
“It’s important for women to have the facts,” said Dr. Karin B. Michaels of Brigham and Women’s Hospital in Boston. Michaels is lead author of the study.
A 2003 expert panel convened by the National Cancer Institute concluded that no evidence supports a link between abortion and breast cancer, she said, “and our study is very much in line with that.”
But Karen Malec, president of the Coalition on Abortion/Breast Cancer, took issue with the findings. “Clearly (the cancer institute) must suspect a link, or else they know that a link really exists,” she said. “Why else would they continue to pay for these studies?”
The coalition uses the purported link as an argument against abortion.
The new results, reported in the Archives of Internal Medicine, are from the Nurses’ Health Study, which enrolled 105,716 women to examine a variety of health issues.
Beginning in 1993, and every two years afterward, Michaels and her colleagues questioned the women – who were ages 29 to 46 at enrollment – about abortions, miscarriages and breast cancer.
They found that 16,118 had had at least one abortion and 21,753 had had a miscarriage, also known as a spontaneous abortion. The team found 1,458 new cases of breast cancer among all the women; the risk was the same among those who had had an abortion and those who had not.
The design of the study, Michaels said, was much more reliable than previous studies, which started with women who’d had breast cancer and asked them if they had undergone an abortion. Such studies introduce “recall bias,” she said, because women with breast cancer are more likely to reveal details of an abortion if they think it might be related to their condition.