In fact, the soundest studies–those with the most rigorous methodology–had in fact found no such increased risk, and today an exhaustive study confirms that. According to a study published in the Archives of Internal Medicine, a journal of the American Medical Association, neither abortion nor miscarriage appears to increase the risk of breast cancer.
On paper, you might actually expect abortion to raise the risk of breast cancer. After all, women younger than age 35 who give birth have a reduced lifetime risk of breast cancer; another way of saying that is that women who do not give birth–which tends to happen after an abortion–have an elevated risk. Also, pregnancy seems to spur breast cells to differentiate, which counteracts the effect of pregnancy hormones that make cells divide and multiply (too much of which equals cancer). If the pregnancy is terminated, breast cells might not differentiate enough to counter the pro-multiplication effect of pregnancy hormones.
Whatever happens on paper, the scientists found that it did not happen in real women. Led by Karin B. Michels of Brigham and Women’s Hospital, they studied 105,716 women in the Nurses’ Health Study II, all of whom answered questions every two years about whether and at what age they had had miscarriages or abortions and whether they had been diagnosed with breast cancer. A total of 16,118 women (15 percent) had an abortion, and 1,458 got breast cancer. But there was “no association between induced abortion and breast cancer incidence,” the scientists write.
