ASCL1 and small cell lung carcinoma: Four molecular subtypes of SCLC have been described on the basis of differential expression of four master transcription factors: ASCL1 (SCLC-A), NeuroD1 (SCLC-N), POU2F3 (SCLC-P), and YAP1 (SCLC-Y) (Fig. 5) (109).