Objective: Our prospective studies in Japan have found an increased ovarian cancer incidence in women with ovarian endometrioma (standardized incidence ratio, 8.95; 95% confidence intervals, 4.12-5.3). The risk increased with increasing age at ovarian endometrioma diagnosis. The goal of this study was to define the risk factor(s) of ovarian cancer development in a Japanese population with ovarian endometrioma. We also analyzed whether the predisposition toward ovarian cancer is limited to endometrioid and clear cell carcinoma.
Study design: A total of 6398 participants at 212 participating hospitals in Shizuoka, Japan, were enrolled in the Shizuoka Cohort Study on Endometriosis and Ovarian Cancer (SCSEOC) Trial, which had prospective and retrospective components. The follow-up period was up to 17 years (median, 12.8 years). The risks of development of ovarian cancer were assessed in 6398 women with ultrasonographically diagnosed ovarian endometriomas. Cox proportional-hazards regression function was used to estimate impact in terms of risk factors and possible development of ovarian cancer.
Results: The prospective study demonstrated that 46 (0.72%) of 6398 women developed histologically proven ovarian cancer and were operated upon during follow-up. Clear cell carcinoma (39%) and endometrioid adenocarcinoma (35%) were commonly observed among women with ovarian cancer. By multivariate analysis, tumor size > or =9 cm in diameter and postmenopausal women were independent predictive factors of patients with development of ovarian cancer.
Conclusions: Some endometriosis lesions may predispose to clear cell and endometrioid ovarian cancers. Advancing age and the size of endometriomas were independent predictors of development of ovarian cancer among women with ovarian endometrioma.