Ovarian cancer prognosis in women with endometriosis: a retrospective nationwide cohort study of 32,419 women.

Background: Contradicting results regarding ovarian cancer prognosis in women with endometriosis have been reported in the literature. Owing to the small sample size of previous studies, larger studies are required to elucidate the role of endometriosis in ovarian cancer prognosis.
Objective: This study aimed to evaluate the survival rate in women with ovarian cancer with or without histologically proven endometriosis in a Dutch population-based cohort.
Study Design: All women with ovarian cancer diagnosed between 1990 and 2015 were identified from the Netherlands Cancer Registry. We linked these women with the Dutch nationwide registry of histopathology and cytopathology (Pathologisch-Anatomisch Landelijk Geautomatiseerd Archief) to identify all women with histologically proven endometriosis. We compared the prognosis of patients with ovarian cancer with and without histologically proven endometriosis. Primary outcome was the overall survival with subgroup analyses stratified by histologic ovarian cancer subtype and stage. Multivariable Cox proportional hazard analysis was used to estimate hazard ratios with 95% confidence intervals.
Results: We included 32,419 patients with ovarian cancer, of whom 1979 (6.1%) had histologically proven endometriosis. The median age of histologic endometriosis diagnosis was 53 years (interquartile range, 46-62). Of all women with ovarian cancer and endometriosis, 81.2% received a diagnosis of synchronous endometriosis and ovarian cancer. The endometriosis cohort was younger at ovarian cancer diagnosis, had more favorable tumor characteristics, and more often had surgical treatment for ovarian cancer than the women without endometriosis. These variables were included in the multivariable model as confounders. Women with histologically proven endometriosis had a significantly better prognosis in both crude and adjusted analyses (hazard ratio, 0.46; 95% confidence interval, 0.43-0.49; P<.0005, and adjusted hazard ratio, 0.89; 95% confidence interval, 0.83-0.95; P<.05, respectively).
Conclusion: Women with ovarian cancer and histologically proven endometriosis had longer overall survival than women with ovarian cancer without endometriosis, even after adjustment for confounders. Future studies on ovarian cancer treatment and prognosis should consider stratifying by endometriosis status to elucidate its role. Furthermore, women diagnosed as having ovarian cancer and concurrent endometriosis should be explained the role of endometriosis in ovarian cancer survival.
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