Poorly differentiated mucinous carcinoma with signet ring cells in an ovarian endometriotic cyst: a case report

BACKGROUND: Ovarian signet ring cell carcinomas are predominantly metastatic. Cases coexisting with endometriotic cysts are extremely rare, and are supposed to be primary. However, such cases have not been well-documented to date. CASE PRESENTATION: A 46-year-old Chinese woman had an incidental small nodule in the right ovarian endometriotic cyst. She underwent a staging surgery due to an unexpected ovarian carcinoma from her frozen section. Laparotomy exploration, MRI and gastrointestinal endoscopy revealed no other abnormalities in the abdominal organs. She had a pelvic recurrence at 7 months and was alive with disease for 13 months at present. Gross examination showed a small mural nodule (l.0 × 0.5 × 0.2 cm) in the wall of the right ovarian cyst (18x15x14 cm). Microscopically, the neoplastic cells arranged in solid nests, crowded small irregular glands and scattered single cells. They had abundant cytoplasmic mucin and contained a significant component of signet ring cells. The stroma was desmoplastic and occasionally contained extracellular mucin deposits. The surrounding endometriotic cyst had several foci of atypical surface epithelium (atypical endometriotic cyst) that was continuous with the mucinous carcinoma. Immunohistochemistry demonstrated that the tumor cells were diffusely positive for CK7 and negative for CK20 and CDX2. CONCLUSIONS: Primary ovarian poorly differentiated mucinous carcinoma with signet ring cells can occur in an atypical endometriotic cyst. This rare case addresses the necessity of careful and extensive pathological examination on large ovarian endometriotic cysts.