Ciliated muconodular papillary tumor of the lung harboring BRAF V600E mutation and p16^INK4a overexpression without proliferative activity may represent an example of oncogene-induced senescence

Ciliated muconodular papillary tumor (CMPT) is a rare peripheral lung tumor that shows puzzling histologic features encompassing metaplastic and neoplastic nature. This type of tumor is occasionally misdiagnosed as lung adenocarcinoma clinically and pathologically, and its pathogenic mechanism has not been well characterized. We experienced a case of CMPT in a 73-year-old male and performed targeted deep sequencing to characterize its molecular features. The tumor was an ill-defined, subpleural, and non-endobronchial nodule showing glandular and papillary proliferation of mucous cells, ciliated columnar cells, and basal cells without any cytologic atypia. Abundant intra-alveolar mucin surrounded the main lesion. The patient was well without recurrence throughout 36 months of follow-up. Our case harbored BRAF V600E mutation and strongly expressed p16^INK4a without proliferative activity, representing senescence and indolent biologic behavior. Overall, the results of this study indicate that BRAF V600E mutation might be the driver for tumorigenesis of CMPT and eventually leads to oncogene-induced senescence of this tumor.