MONDAY, April 23 (HealthDay News) -- Although women have a lifetime reduction in breast cancer risk if they have a full-term pregnancy before the age of 35, those who have a spontaneous or induced abortion are not at higher risk of developing the disease compared with the general female population, according to the results of a study published in the April 23 issue of the Archives of Internal Medicine.
Karin B. Michels, Ph.D., of Harvard Medical School and Brigham and Women's Hospital in Boston, and colleagues conducted a study of 105,716 women aged 29 to 46 years old who were followed up from 1993 until 2003. During the follow-up period, there were 1,458 newly diagnosed cases of invasive breast cancer.
Among the study cohort, 16,118 women (15 percent) had a history of induced abortion, and 21,753 (21 percent) had a history of miscarriage. There was no association between single or multiple abortions and the likelihood of developing breast cancer.
"We observed associations in two subgroups, an association between induced abortion and progesterone receptor-negative breast cancer and an inverse association between spontaneous abortion before the age of 20 years and breast cancer incidence," the authors write. They caution that "subgroup analyses have to be interpreted cautiously, especially if the strata are small. No obvious mechanisms can be provided for these subgroup findings; thus, chance has to be considered as a possible explanation."
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