Induced abortion and breast cancer among parous women: a Danish cohort study

Objective We investigated whether induced abortion is associated with breast cancer when lifestyle confounders, including smoking and alcohol consumption, are adjusted for. Design. Prospective cohort study. Setting Danish women from the Diet, Cancer and Health study. Population A total of 25576 women. Methods We obtained exposure data from baseline questionnaires filled in by the women between 1993 and 1997. Information on breast cancer and emigration was retrieved from Danish national registries. The study power was approximately 85% when applying a minimum detection hazard ratio of 1.2. Main outcome measures Long-term effects of induced abortion on the risk of breast cancer among women above 50years of age. Results During a follow up of approximately 12years, 1215 women were diagnosed with breast cancer. When comparing parous women who had an abortion with parous women who never had an abortion, there was no association between breast cancer risk and induced abortion (ever vs. never), with a hazard ratio 0.95 (95% confidence interval 0.831.09), regardless of whether the abortion occurred before the first birth (hazard ratio 0.86; 95% confidence interval 0.651.14), or after the first birth (hazard ratio 0.97; 95% confidence interval 0.841.13). Conclusions Our study did not show evidence of an association between induced abortion and breast cancer risk.