Ciliated muconodular papillary tumor of the lung harboring ALK gene rearrangement: Case report and review of the literature.

Ciliated muconodular papillary tumor (CMPT) of the lung is an extremely rare peripheral tumor of the lung. The pathogenesis of CMPT is still unknown, and its nature as a benign tumor or reactive process is still open to discussion. Recent studies have identified BRAF, EGFR and AKT1 mutations in CMPT, which would support a true neoplastic process. Here for the first time, we report a case of morphologically typical CMPT harboring ALK gene rearrangement to further provide convincing evidence that CMPT is a neoplastic process rather than a reactive lesion. The patient was a 59-year-old woman, characterized by a circumscribed tubulopapillary tumor consisting of ciliated columnar cells, mucous cells, and basal cells, accompanied with peripheral abundant extracellular mucin. The tubulopapillary architecture with abundant extracellular mucin is mimicking adenocarcinoma. The tumor cells were immunoreactive for cytokeratin 7, thyroid transcription factor-1, whereas p40 and p63 highlighted the presence of basal cells. The ALK gene rearrangement was detected using fluorescence in situ hybridization and Ventana immunohistochemistry platform. To our knowledge, this is the first study to confirm CMPT harboring ALK gene rearrangement.