Prevalence of Endometriosis in Malignant Epithelial Ovarian Tumor.

BACKGROUND: The present study aims to assess the prevalence and histological characteristics of endometriosis in different types of ovarian surface epithelial tumors. METHODS: Microscopic slides of 110 ovarian tumors (89 malignant and 21 borderlines) were reviewed from 2008 to 2013 in two major gynecological centers affiliated with the Shiraz University of Medical Sciences, Shiraz, Iran. The presence or absence of endometriosis and transitions from atypical endometriosis to carcinoma were also histologically evaluated. Chi-square and t-test were used to compare the study groups. RESULTS: The mean age of the patients was 49.93 ± 9.36 years in the Endometriosis-Associated Ovarian Carcinomas (EAOC) group and 50.18 ± 12.8 years in the non-EAOC group. Among the 110 patients, 28 (25.4%) had endometriosis. According to ovarian cancer subtype 67% (4/6) of clear cell adenocarcinoma, 65% (11/17) of endometrioid adenocarcinoma, 28% (7/25) of low grade serous adenocarcinoma, 4% (1/25) of high grade serous adenocarcinoma, 30% (4/13) of borderline serous tumor, and 25% (1/4) of mixed carcinoma had endometriosis. None of the mucinous borderline tumors and mucinous adenocarcinoma cases had endometriosis. Moreover, 23 cases had typical endometriosis, while 14 had atypical endometriosis. On the other hand, 19 cases had both typical and atypical endometriosis. Furthermore, transition from atypical endometriosis to carcinoma was seen in 11 cases. CONCLUSION: Clear cell and endometrioid carcinoma are the most common types of EACO. Atypical endometriosis was more commonly seen in endometrioid and clear cell carcinomas which are included in type I ovarian cancer. Thus, it can be concluded that atypical endometriosis is a precursor for type I ovarian cancer.