Background: A recent meta-analysis concluded that there was no overall association between estrogen replacement therapy (ERT) and risk of epithelial ovarian cancer. However, several subsequent studies have suggested that long-term ERT could increase ovarian cancer risk.
Methods: We prospectively examined the association of ERT with epithelial ovarian cancer among 31,381 postmenopausal women in Iowa followed for 15 years.
Results: Women who were using ERT at baseline had an elevated multivariate-adjusted relative risk of ovarian cancer (1.7; 95% confidence interval [CI] = 1.1-2.8) compared with never-users. Risk was higher among women who had been using ERT at baseline for more than 5 years (2.5; CI = 1.4-4.5). A time-dependent analysis likewise yielded a relative risk of 1.7 for current ERT use. Former ERT use was not associated with ovarian cancer incidence.
Conclusions: Long duration of ERT use after menopause could increase the risk of epithelial ovarian cancer.