Ovarian Carcinoma Presenting Mucoepidermoid Carcinoma-Like Features in Association With Seromucinous Borderline Tumor: A Real Seromucinous Carcinoma?

Ovarian seromucinous carcinoma is generally classified within the spectrum of endometrioid carcinoma. We report a rare ovarian carcinoma with mucoepidermoid carcinoma-like features arising in direct association with a seromucinous borderline tumor. A 56-year-old postmenopausal female presented with a 10-cm pelvic multilocular cystic tumor and markedly elevated carbohydrate antigen 19-9. Histopathological examination showed a seromucinous borderline tumor with transition to invasive carcinoma composed of mucinous epithelial cells and p40-positive intermediate-like cells. The tumor was diffusely positive for PAX8 and negative for cytokeratin 20, supporting Mullerian differentiation. The p40-positive cell population persisted in the borderline, invasive, and para-aortic lymph node metastatic components. Comprehensive genomic profiling identified KRAS p.G12D without CTNNB1, PTEN, or ARID1A mutations. The patient developed platinum-resistant recurrence and died 11 months after diagnosis. This case is compatible with a potential endometriosis-independent pathway from seromucinous borderline tumor to an aggressive mucoepidermoid-like carcinoma.