RT Journal Article SR Electronic T1 OP017/#81 Endometrial cancer prognosis in women with endometriosis and adenomyosis. A retrospective nationwide cohort study of 40,847 women JF International Journal of Gynecologic Cancer JO Int J Gynecol Cancer FD BMJ Publishing Group Ltd SP A18 OP A18 DO 10.1136/ijgc-2021-IGCS.34 VO 31 IS Suppl 4 A1 M Hermens A1 A Van Altena A1 M Van Der Aa A1 J Bulten A1 H Van Vliet A1 A Siebers A1 R Bekkers YR 2021 UL http://ijgc.bmj.com/content/31/Suppl_4/A18.1.abstract AB Objectives The effect of endometriosis/adenomyosis on the prognosis of its related endometrial cancer remains unclear. Therefore, we aim to compare endometrial cancer survival in women with or without histological proven endometriosis or adenomyosis.Methods Women with endometrial cancer between 1990–2015 were identified from the Netherlands Cancer Registry (NCR). This data was linked to the Dutch pathology database (PALGA) to select all women with histological proven endometriosis or 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) with 95% confidence intervals (CI).Results We included 1,708 women with endometrial cancer and endometriosis/adenomyosis and 39,139 women without endometriosis/adenomyosis. Women in the endometriosis/adenomyosis cohort were younger at endometrial cancer diagnosis, had earlier disease stage and more often had endometrioid endometrial cancer with low grade tumors. The 5-year survival rate in the endometriosis/adenomyosis cohort was 84.8% (95%CI 84.6–88.1) and 71.6% (95%CI 71.1–72.0) in the control cohort, p<0.0005. Univariate analysis resulted in a crude HR for overall survival of 0.63 (95%CI 0.59–0.69). Significant confounding factors are reported in table 1. Correction for these confounders resulted in a HR of 0.98 (95%CI 0.90–1.06), p=0.867 (table 1).View this table:Abstract OP017/#81 Table 1 Hazard rations of overall survival among women with endometrial cancer in univariate and multivariate analysis (n=35,549)Conclusions 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 is correlated to stage, grade, age, and histology, but not to the presence of endometriosis/adenomyosis.