Low-grade epithelial tumor of pituitary region with dominant papillary architecture is extremely rare. We describe a case of 20-year female who had a recurrent nonfunctioning pituitary tumor. Histologic examination revealed a low-grade epithelial tumor with predominant papillary architecture, lined by cuboidal to columnar epithelial cells. The tumor cells were immunpositive for cytokeratin (CK), CK7, epithelial membrane antigen, carcinoembryonic antigen and showed diffuse and strong nuclear positivity for thyroid transcription factor 1. They were negative for neuroendocrine markers and pituitary hormones. Ki-67 proliferation index was low (1%). Ultrastructural examination revealed presence of microvilli, intercellular tight junctions, and keratin filaments within the tumor cells and lack of neurosecretory granules. No lesion was identified in thyroid or lung on systemic evaluation. On the basis of the morphology, immunophenotype, ultrastructural findings, and diffuse thyroid transcription factor 1 positivity, this tumor may represent an epithelial variant of pituicytoma with dominant papillary architecture. This type of differentiation is extremely rare, and to the best of our knowledge, has not been described previously in the literature.
Adult Biomarkers, Tumor