Endometriosis-associated epithelial ovarian cancer is a more complicated disease than we suspected before.

Objective: Endometriosis-associated epithelial ovarian cancer (EOC) often includes clear cell carcinoma and endometrioid-type carcinoma. Due to the low incidence of primary mucinous EOC and absence of association between endometriosis and primary mucinous EOC, we present an unusual endometriosis-associated mixed mucinous and endometrioid adenocarcinoma arising from the same ovary.

Case Report: A 54-year-old woman had an abdominal palpable mass for months. Medical and surgical history, as well as preoperative surveys was unremarkable, except of presence of a pelvic mass. She underwent an exploration laparotomy, and a 22-cm right ovarian tumor was found. Grossly, right ovarian tumor containing brownish cloudy cystic fluid 2450 ml and an apparent 4 × 4 × 2 cm-sized papillary growth. Microscopically, a confluent glandular and infiltrative pattern presented endometrioid adenocarcinoma, and cells with intracytoplasmic mucin and stratified elongated epithelial cells presented mucinous adenocarcinoma. Surgico-pathological stage was FIGO IIIA due to tumor invading to the peritoneum above the pelvis. Postoperatively, the dose-dense chemotherapy was applied with uneventful outcome.

Conclusion: This is a rare case, composed with mixed mucinous and endometrioid adenocarcinoma of the same ovary, suggesting that careful pathological diagnosis of endometriosis-associated EOC is needed.