Endometrial Cancer Incidence in Endometriosis and Adenomyosis

Simple Summary Previous research shows that women with endometriosis and adenomyosis have an increased ovarian cancer risk. However, it is unclear whether these women have an increased risk of developing uterine cancer. This information is of key importance to women with endometriosis or adenomyosis. Therefore, this study aims to assess the uterine cancer risk in women with endometriosis or adenomyosis in a large population. Abstract Women with histologically proven endometriosis/adenomyosis have an increased risk of ovarian cancer. Small studies show conflicting results on the endometrial cancer risk in women with endometriosis/adenomyosis. Therefore, we assessed the incidence of endometrial cancer in women with histologically proven endometriosis or adenomyosis. We performed a population-based retrospective cohort study of 129,862 women with histologically proven endometriosis/adenomyosis, matched with 132,700 women with a nevus selected from the Dutch pathology registry between 1990 and 2015. Histology results for endometrial cancer were retrieved. Crude and age-adjusted odds ratios for endometrial cancer were estimated. In the endometriosis/adenomyosis group, 1827 (1.4%) women had a histological report on endometrial cancer, and in the nevus group, 771 (0.6%) women. The age-adjusted OR for endometrial cancer was 2.58 (95%CI 2.37–2.81). After excluding the first year of follow-up, the age-adjusted OR was 0.76 (95%CI 0.63–0.92), indicating that endometrial cancer is most often found at time of histological diagnosis of endometriosis/adenomyosis. In around 20% of the endometrial cancer cases, the endometrial cancer was not recognized until after hysterectomy. Of these women, 35% had no prior (micro)curettage or biopsy. This study shows an increased incidence of endometrial cancer in women with histologically proven endometriosis and adenomyosis.