**7. Prognosis of endometriosis-associated ovarian cancer**

Clear cell adenocarcinoma is known to be associated with chemoresistancy and a poor prognosis (Itamochi, 2008). However, most reports analyzing the prognosis of endometriosis-associated ovarian carcinomas (including mostly endometrioid adenocarcinoma and few clear cell carcinoma samples) have shown that endometriosisassociated ovarian carcinomas presented at younger ages, in lower grades and stages, and had significantly better overall survival compared with age-matched controls without endometriosis (Erzen, 2001; Kumar, 2011; Melin, 2011 ; Orezzoli, 2008). However, recent studies from various countries indicate that clear cell carcinomas consist of heterogenous tumors with gene alterations, such as HER2 or Met gene amplification (Tan, 2011 ; Yamamoto, 2011; Yamashita, 2011). Therefore, clear cell carcinomas as a subtype are considered to have a worse prognosis than endometrioid adenocarcinomas, especially in Asian cases (Lee, 2011). Recently, the first international symposium of ovarian clear cell carcinoma concluded that although patients with low-stage clear cell carcinoma had a better prognosis than matched controls with high-grade serous carcinoma, high-stage clear cell carcinoma cases had the worst prognosis (Anglesio, 2010). Thus, alternative therapy, such as molecular targeted therapy, should be applied to these aggressive tumors, and a further understanding of the basic biology of the endometriosis-cancer progression, especially the role of oxidative stress, is necessary to prevent carcinogenesis in endometriosis patients (Aris, 2010).
