Clinicopathological Characteristics of Metaplastic Papillary Tumor of the Fallopian Tube.

ABSTRACT

Metaplastic papillary tumor (MPT) of the fallopian tube is a very uncommon lesion, displaying papillary growth of bland-appearing cells with abundant, eosinophilic cytoplasm and mucinous metaplasia. It is difficult for pathologists to determine whether to categorize this lesion as a metaplastic proliferative lesion or a true neoplasm. We recently experienced a case of tubal MPT and initiated a comprehensive review of previously published cases with thorough analysis of clinicopathological characteristics. MPT is typically related to pregnancy, but we describe the first case of pregnancy-unrelated, incidentally detected tubal MPT in a 51-year-old woman who underwent surgery for endometrial cancer. The MPT consisted of small papillary formations with epithelium consisting of nonciliated, columnar cells with abundant eosinophilic cytoplasm arranged as either a single layer or pseudostratified layer. The stroma had a myxoid appearance. Intraluminal and extracellular mucin and floating papillary tufts were observed. Nuclei of the epithelial lining cells were centrally located, rounded or oval, and displayed intranuclear pseudoinclusions or grooves. The MPT cells were positive for paired box 8, epithelial membrane antigen, and cytokeratin. Interestingly, Wilms tumor 1 (WT1) protein was localized within the cytoplasm of MPT cells. Furthermore, the MPT cells did not express phosphatase and tensin homolog deleted on chromosome 10 (PTEN). In summary, MPT of the fallopian tube is a very unusual, distinctive entity displaying unique histopathological features and immunophenotype. Our observation of cytoplasmic WT1 expression and loss of PTEN expression in tubal MPT suggests its neoplastic nature and raises the possibility of WT1 or PTEN involvement in the development of MPT.