Contradicting results regarding ovarian cancer prognosis in women with endometriosis have been reported in the literature. Due to the small sample size of previous studies, larger studies are required to elucidate the role of endometriosis on ovarian cancer prognosis.
To evaluate the survival rate in women with ovarian cancer with or without histological proven endometriosis in a Dutch population-based cohort.
All women with ovarian cancer diagnosed between 1990 and 2015 were identified from the Netherlands Cancer Registry (NCR). We linked these women with the Dutch nationwide registry of histopathology and cytopathology (PALGA) to identify all women with histological proven endometriosis. We compared prognosis of ovarian cancer patients with and without histological proven endometriosis. Primary outcome was overall survival with subgroup analyses stratified by histological ovarian cancer subtype and stage. Multivariable Cox proportional hazard analysis was used to estimate hazard ratios (HRs) with 95% confidence intervals (CI).
We included 32,419 ovarian cancer patients, of whom 1,979 (6.1%) had histological proven endometriosis. The median age of histological endometriosis diagnosis was 53 years (IQR 46-62). Of all women with ovarian cancer and endometriosis 81.2% had a synchronous endometriosis and ovarian cancer diagnosis. The endometriosis cohort was younger at ovarian cancer diagnosis, had more favorable tumor characteristics and more often had surgical treatment for ovarian cancer when compared to the women without endometriosis. These variables were included in the multivariable model as confounders. Women with histological proven endometriosis had a significantly better prognosis in both crude and adjusted analysis (HR 0.46 (95%CI 0.43-0.49), p<0.0005 and adjusted HR 0.89 (95%CI 0.83-0.95), p<0.05).
Women with ovarian cancer and histological proven endometriosis had longer overall survival when compared to 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 with ovarian cancer and concurrent endometriosis should be explained the role of endometriosis on ovarian cancer survival.

Copyright © 2020. Published by Elsevier Inc.

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