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 25,576 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 50 years of age. RESULTS: During a follow up of approximately 12 years, 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 0.83-1.09), regardless of whether the abortion occurred before the first birth (hazard ratio 0.86; 95% confidence interval 0.65-1.14), or after the first birth (hazard ratio 0.97; 95% confidence interval 0.84-1.13). CONCLUSIONS: Our study did not show evidence of an association between induced abortion and breast cancer risk.

Multiple miscarriages are associated with the risk of ovarian cancer: results from the European Prospective Investigation into Cancer and Nutrition.

While the risk of ovarian cancer clearly reduces with each full-term pregnancy, the effect of incomplete pregnancies is unclear. We investigated whether incomplete pregnancies (miscarriages and induced abortions) are associated with risk of epithelial ovarian cancer. This observational study was carried out in female participants of the European Prospective Investigation into Cancer and Nutrition (EPIC). A total of 274,442 women were followed from 1992 until 2010. The baseline questionnaire elicited information on miscarriages and induced abortions, reproductive history, and lifestyle-related factors. During a median follow-up of 11.5 years, 1,035 women were diagnosed with incident epithelial ovarian cancer. Despite the lack of an overall association (ever vs. never), risk of ovarian cancer was higher among women with multiple incomplete pregnancies (HR(≥4vs.0): 1.74, 95% CI: 1.20-2.70; number of cases in this category: n = 23). This association was particularly evident for multiple miscarriages (HR(≥4vs.0): 1.99, 95% CI: 1.06-3.73; number of cases in this category: n = 10), with no significant association for multiple induced abortions (HR(≥4vs.0): 1.46, 95% CI: 0.68-3.14; number of cases in this category: n = 7). Our findings suggest that multiple miscarriages are associated with an increased risk of epithelial ovarian cancer, possibly through a shared cluster of etiological factors or a common underlying pathology. These findings should be interpreted with caution as this is the first study to show this association and given the small number of cases in the highest exposure categories.