Two tumors with combined features of bronchiolar adenoma/ciliated muconodular papillary tumor and sclerosing pneumocytoma.

Abstract

Bronchiolar adenoma/ciliated muconodular papillary tumor (BA/CMPT) and sclerosing pneumocytoma (SP) are both rare and morphologically unique peripheral lung tumors with indolent behavior. These tumors have not been previously described as showing overlapping morphologic features and are generally genetically distinct. Two cases were recently encountered that show hybrid morphologic features between BA/CMPT and SP, and the morphology and immunophenotype are described in detail. Both cases showed interstitial round cells typical of SP (TTF1+, EMA+), as well as areas more typical of BA/CMPT. One case showed BRAFV600E expression in the BA/CMPT areas but not in the SP-like cells. Although it is possible that these cases represent collision tumors or are examples of unusual metaplastic epithelial changes in SP, they also raise the possibility that these 2 entities could occasionally coexist in true hybrid tumors.