Breast cancer incidence after hormonal infertility treatment in Sweden: a cohort study.

Abstract

To assess the impact of infertility treatment with causes of infertility on incidence of breast cancer. Historical prospective cohort study of 1135 women attending major university clinics for treatment of infertility in Sweden, 1961-1976. Women were classified as users of clomiphene citrate or gonadotropins, or a combination of both therapies. Standardized incidence ratios were calculated to estimate relative risk of breast cancer. We observed 54 cases of breast cancer during 1961-2004, which did not significantly exceed those expected. Users of high-dose clomiphene citrate had an almost 2-fold increased risk (standardized incidence ratio, 1.90; 95% confidence interval, 1.08-3.35). This association was more pronounced among women referred for nonovulatory factors, with 3-fold increased risk (standardized incidence ratio, 3.00; 95% confidence interval, 1.35-6.67). No overall increased risk for breast cancer was shown with infertility treatment. Women with nonovulatory causes treated with high-dose clomiphene citrate therapy may have an elevated risk for breast cancer.