LAUSR

Ciliated muconodular papillary tumors (CMPTs) are rare peripheral lung lesions, characterized by papillary architecture and ciliated columnar cells admixed with mucous cells and basal cells. Only about 50 cases have been reported to date and is categorized as a benign neoplasm. In this article, we report an extremely rare case of 79-year-old man with a CMPT that developed in his right upper lobe. The central region of the tumor showed features of classic CMPT, while marginal area of the tumor showed the characteristics of invasive lung cancer. In central classic CMPT region, the ciliated, basal, and mucous cells were positive for thyroid transcription factor-1, cytokeratin 7 (CK7), and NapsinA. Basal cells were positive for CK5/6 and p40. Mucous cells were weakly positive for MUC2 and MUC5AC. However, CK5/6 and p40 were negative in the peripheral malignant area. Both of the benign and malignant regions had an EGFR driver mutation in exon 21. We concluded that this tumor was an extremely rare malignant case of CMPT.