Endometrial cancer risk after fertility treatment: a population-based cohort study

Purpose Using data from a large population-based cohort of women with fertility problems in Denmark, we examined the association between use of fertility drugs and endometrial cancer incidence. Methods Women aged 20-45 years living in Denmark during 1 January 1995-31 December 2017 and diagnosed with fertility problems (i.e., subfertile women) were identified from the Danish Infertility Cohort. Information on use of fertility drugs, endometrial cancer, covariates and vital status was obtained from various Danish national registers. Cox proportional hazard models were used adjusted for calendar year of study entry, highest level of education, parity status, hormonal contraceptive use, obesity and diabetes mellitus. Results Of the 146,104 subfertile women, 129,478 (88.6%) were treated with fertility drugs. During a median follow-up of 10.1 years, 119 women were diagnosed with endometrial cancer. Use of any fertility drugs was not associated with an increased rate of overall (HR 0.82; 95% CI 0.50-1.34) or type I endometrial cancer (HR 1.08; 95% CI 0.60-1.95). No associations between use of specific types of fertility drugs and endometrial cancer were observed. No marked associations were observed according to cumulative dose of specific fertility drugs, parity status, or with increasing follow-up time. Conclusions No marked associations between use of fertility drugs and risk of endometrial cancer were observed. The relatively young age of the cohort at end of follow-up, however, highlights the need for longer follow-up of women after fertility drug use