Ovarian stimulation and risk of breast cancer in Swedish women

Objective: To investigate whether ovarian stimulation for treating infertility is associated with the risk of breast cancer. Design: Nationwide register-based cohort study. Setting: Not applicable. Patient(s): In a cohort of 1,340,211 women who gave birth 1982-2012, we investigated the relationship between assisted reproductive technology (ART) and incidence of breast cancer. Associations between any ovarian stimulation since 2005 and breast cancer incidence were studied in a separate cohort of 1,877,140 women born 1960-92. Both cohorts were followed through 2012. Intervention(s): None. Main Outcome Measure(s): Hazard ratios (HRs) and 95% confidence intervals (CIs) for breast cancer. Result(s): There was no increased risk of breast cancer in women who gave birth after ART compared with women who gave birth after spontaneous conception (adjusted HR, 0.84; 95% CI, 0.74-0.95). The incidence of breast cancer was not increased among women who received controlled ovarian stimulation or among women who received other hormonal fertility treatments since 2005, regardless of live birth (adjusted HR, 0.86; 95% CI, 0.69-1.07; and adjusted HR, 0.79; 95% CI, 0.60-1.05, respectively). Conclusion(s): No increased incidence of breast cancer was found among women who had gone through ovarian stimulations, including ART. These results are consistent with other studies and reassuring given the widespread and increasing use of ART. (C) 2017 The Authors. Published by Elsevier Inc. on behalf of the American Society for Reproductive Medicine.