YAP1 and small cell lung carcinoma: Previously investors had initially identified four main molecular subtypes of SCLC by the expression levels of transcription factors in recent years: ASCL1 (SCLC-A), NEUROD1 (SCLC-N), POU2F3 (SCLC-P), and YAP1 (SCLC-Y)48, 49.