POU2F3 and small cell lung carcinoma: Although the role of YAP1 as a subtype defining transcription factor for SCLC remains controversial, the existence of a subset of SCLC tumors that lack expression of NEUROD1, ASCL1, or POU2F3 and characteristically exhibit low expression of neuroendocrine markers is well recognized and has been reproducibly identified in several SCLC patient cohorts (8, 12, 13).