Loss of YAP1 defines neuroendocrine differentiation of lung tumors.

YAP1, the main Hippo pathway effector, is a potent oncogene and is overexpressed in non-small-cell lung cancer (NSCLC); however, the YAP1 expression pattern in small-cell lung cancer (SCLC) has not yet been elucidated in detail. We report that the loss of YAP1 is a special feature of high-grade neuroendocrine lung tumors. A hierarchical cluster analysis of 15 high-grade neuroendocrine tumor cell lines containing 14 SCLC cell lines that depended on the genes of Hippo pathway molecules and neuroendocrine markers clearly classified these lines into two groups: the YAP1-negative and neuroendocrine marker-positive group (n = 11), and the YAP1-positive and neuroendocrine marker-negative group (n = 4).