We aim to compare endometrial cancer survival in women with or without histological proven endometriosis or adenomyosis. We identified all women with endometrial cancer between 1990-2015 from the Netherlands Cancer Registry (NCR). Data was linked to the Dutch pathology database (PALGA) to select all women with histological proven endometriosis/adenomyosis. Overall survival was compared between women with endometrial cancer with or without endometriosis/adenomyosis. We used multivariable Cox proportional hazard analysis to estimate hazard ratios (HRs). We included 1,701 women with endometrial cancer and endometriosis/adenomyosis, of whom 1,236 (72.7%) women had adenomyosis, 320 (18.8%) had endometriosis and 145 (8.5%) had both. We compared these women to 39,139 women with endometrial cancer without endometriosis/adenomyosis. Women in the combined endometriosis/adenomyosis cohort were younger at endometrial cancer diagnosis, had earlier disease stage, more often had endometrioid endometrial cancer and low grade tumors. The 5-year survival rate in the combined endometriosis/adenomyosis cohort was 84.8% (95%CI 84.6-88.1) and 71.6% (95%CI 71.1-72.0) in the non-endometriosis/adenomyosis cohort. Univariable analysis resulted in a crude HR of 0.63 (95%CI 0.59-0.69). Significant confounding factors were age, stage, cancer subtype, histological grading, surgery and chemotherapy rate. Correction for these confounders resulted in a HR of 0.98 (95%CI 0.90-1.06). Including endometriosis/adenomyosis status as a categorical factor resulted in similar HRs. In conclusion, women with endometrial cancer and histologically proven endometriosis/adenomyosis have a better overall survival when compared to women with endometrial cancer without endometriosis/adenomyosis. This better survival was correlated to stage, grade, age, and histological subtype, but not to the presence of endometriosis/adenomyosis.

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