Ovarian Mixed Epithelial Carcinoma with Extensive Bilateral Fallopian Tubes Metastases by the Low-grade Serous Carcinoma Component Mimicking Serous Tubal Intraepithelial Carcinoma: Case Presentation and Literature Review

Seromucinous carcinoma of the ovary was a newly defined category in the revised 2014 World Health Organization Classification of Tumors of Female Reproductive Organs. It was defined as a carcinoma composed of predominantly of serous and endocervical-type mucinous epithelium. Foci containing clear cells, and areas of endometrioid and squamous differentiation are not uncommon. It is a rare entity with morphologic and immunophenotypic features overlapping other types of ovarian carcinoma. There are different opinions as to whether it is a distinct entity or a histologic variant of well-established entities. Subsequent, to the writing of this manuscript the WHO 2020 reclassified this tumor as a type of endometrioid carcinoma. Here we present a case of seromucinous carcinoma of bilateral ovaries that had variable differentiation and morphology at different sites. Tumor in the fallopian tubes, ovarian surfaces, omentum, and peritoneal surfaces displayed predominant features of low-grade serous carcinoma, while the tumor in the ovaries had predominant mucinous carcinoma morphology with a confluent/expansile growth pattern. The mucosal involvement of the fallopian tubes morphologically mimicked serous tubal intraepithelial carcinoma.