Study: No Link Between Abortion and Breast Cancer

Crucial new research has failed to discover a link between induced or spontaneous abortions (miscarriages) and the incidence of breast cancer in pre-menopausal women. According to researchers at Brigham and Women’s Hospital, Harvard Medical School, and Harvard School of Public Health, “In this cohort study of young women, we found no association between induced abortion and breast cancer incidence and a suggestion of an inverse association between spontaneous abortion and breast cancer incidence during 10 years of follow-up.” The results of the research were published in the April 23 issue of the Archives of Internal Medicine.

The report examined the health histories of 105,716 women who were part of the Nurses’ Health Study II (NHSII). All of the women were between the ages of 29 and 46 when the study began in 1993, and they were each subject to follow-up examinations at two-year intervals until 2003. A total of 16,118 women, or about 15 percent of the cohort, reported a history of induced abortion, while 21,753 of them (21 percent) had a history of miscarriage. During the course of the decade-long study, there were 1,458 new cases of breast cancer reported among the women.

“The data from the NHSII provide further evidence of a lack of an important overall association between induced or spontaneous abortions and risk of breast cancer,” the authors conclude. “Among this predominantly pre-menopausal population, neither induced nor spontaneous abortion was associated with the incidence of breast cancer.”

The study did also determine, however, that women under the age of 35 who carry a pregnancy to term appear to have a reduced lifetime risk of breast cancer. Researchers believe that pregnancy may accelerate what is known as breast cell differentiation, a process in which the cells are “assigned” specific roles. “An incomplete pregnancy may not result in sufficient differentiation to counter the high levels of pregnancy hormones that may foster proliferation [of cancer cells],” the authors write. “However, these biological mechanisms are uncertain, and a prematurely terminated pregnancy may not affect breast cancer risk at all.”

According to the researchers, their findings corroborate those of a 2003 international panel that was assembled by the National Cancer Institute. After an extensive review of available research on the matter, the panel concluded that, based on existing evidence, induced abortion is not associated with an increased risk of breast cancer.