Genetic and immunohistochemical analyses of ciliated muconodular papillary tumors of the lung: A report of five cases.

Ciliated muconodular papillary tumors are benign lesions located in the peripheral lung field. Recent studies revealed BRAF and epidermal growth factor receptor gene mutations and anaplastic lymphoma kinase gene rearrangement. Five ciliated muconodular papillary tumors were screened for the BRAF V600E and EGFR mutations via polymerase chain reaction. Immunohistochemical analysis was performed for the detection of the BRAF V600E and anaplastic lymphoma kinase proteins, as well as other markers including phosphorylated extracellular signal-regulated protein kinase. Three tumors (60%) harbored the BRAF V600E mutation. Immunohistochemical analysis confirmed this mutation in all of the tumor cell types. EGFR mutation and immunoactivity of the anaplastic lymphoma kinase protein were not detected. Phosphorylated extracellular signal-regulated protein kinase was negative both in the cytoplasm and nucleus of the BRAF V600E-positive tumors. Mucin 1, mucin 4, thyroid transcription factor 1, and cytokeratin 7 were positive, and mucin 5AC was partially positive, whereas napsin A and cytokeratin 20 were negative. Ciliated muconodular papillary tumor may originate from the terminal bronchioles, and the status of ERK activation reflects its benign behavior.