Fallopian Metaplastic Papillary Tumour: An Atypical Transdifferentiation of the Tubal Epithelium?

A metaplastic papillary tumor of the Fallopian tube is an extremely uncommon condition, with odd and confusing features that make it difficult to categorize as benign or borderline. Here, we summarize all the published cases to date and document the case of a 41-year-old woman diagnosed with this alteration after her last childbirth and ensuing tubal ligation. One of the tubes was bulky and filled with a caramel-like substance encircling a blurry spot. Light microscopy detailed a slender stalk covered by eosinophilic, columnar plump cells, showing atypical nuclei and focal budding. Mitotic figures were absent. The immunohistochemistry panel was positive for pan-cytokeratin, epithelial membrane antigen, cyclin D1, and hormone receptors. Additionally, a proliferation index of less than 5% was rated using Ki-67. The true nature of this tumor (reactive vs neoplastic) is uncertain. Nonetheless, its association with pregnancy suggests an adaptive change, likely similar to the atypical transdifferentiation proposed for Arias-Stella reaction.