Copy number alterations of EGFR and FGFR1 in pulmonary carcinosarcoma

Carcinosarcoma may develop through sarcomatoid changes in a carcinoma, known as epithelial-mesenchymal transition, or may develop from a single cancer stem cell and subsequently diverge into morphologically dissimilar carcinomatous and sarcomatous components. Thus, we tried to elucidate the histogenesis of pulmonary carcinosarcoma, which has not been thoroughly examined. A key approach to the investigation was use of fluorescence in situ hybridization analysis of EGFR and FGFR1, because the carcinomatous component of the carcinosarcoma of the available sample was a squamous cell carcinoma, which tends to harbor copy number gain in EGFR and FGFR1. Consequently, it was postulated that the carcinosarcoma originated from cancer stem cells polysomic for EGFR, and only the carcinomatous component received FGFR1 amplification during divergence into carcinomatous and sarcomatous components.