Risk of Breast Cancer Associated with Induced Abortion

Summary

Certain events of reproductive life, especially completed pregnancies, have been found to influence a woman’s risk of breast cancer. Prior studies of breast cancer in relation to a history of incomplete pregnancies have not provided consistent results. Female residents of three Western Washington counties diagnosed with breast cancer to age 46 years (n = 845 and 961 control women identified through random-digit dialing) were interviewed in detail with regard to their reproductive histories, including the occurrence of induced and spontaneous abortions. Among women who had been pregnant at least once, the risk of breast cancer was 50% higher in those who had experienced an induced abortion than in those women who did not. While the size of this increased risk did not vary by the number of induced abortions or by a history of a prior completed pregnancy, it did vary according to the age at which the abortion occurred, as well as the duration of that pregnancy. Highest risks were observed when the abortion was done prior to 18 years of age (particularly, if it took place after eight weeks of gestation), or at age 30 and beyond. There was no increased risk of breast cancer associated with a prior miscarriage. The data from this and other (although not all) epidemiologic studies support the hypothesis that an induced abortion can adversely influence a woman’s subsequent risk of breast cancer. This question should be re-examined in future studies, with particular attention to the potential hazards related to abortions early in life.