Physicians have known for years that women who have more to term pregnancies appear to be somewhat protected against developing breast cancer. Women whose pregnancies have been interrupted, by spontaneous or induced abortion, did not evidence a protective effect and some studies claimed that they are in fact at a higher risk of developing breast cancer than women who were not pregnant.
It appears probable that hormonal fluxes associated with different stages of pregnancy may have a role in differentiation of breast cells to perform specialized functions within the breast but little is known definitively about these hormonal effects. Whether abortions raise the risk of breast cancer became a matter of contention in the debate over abortion as well as a source of controversy within the medical profession.
It is rare to encounter a woman who would be dissuaded by the fear of developing breast cancer from undergoing an elective abortion; however, it does occasionally play a role in the complicated and difficult process of psychological adjustment and dealing with a new diagnosis of breast cancer.
The most recent study, which examined the association between abortion and breast cancer in 105,716 women who were part of the Nurses' Health Study II (NHSSII), followed thousands of women over ten years and appeared in the April 23 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.
A 2003 international expert panel convened by the National Cancer Institute reviewed and assessed research regarding reproductive events and the risk of breast cancer, and had already concluded that based on existing evidence, induced abortion is not associated with an increased risk of breast cancer.
The NHSSII study concluded that neither induced abortion nor spontaneous abortion (miscarriage) seems to be associated with breast cancer risk in pre-menopausal women. The NHSSII is unlikely to completely end the debate over the possible effects of abortion on the risk of breast cancer later in life; however, it shifts the burden of proof within the debate and will go a long way towards reassuring both women and physicians who remain concerned about this question.