ASCL1 and small cell lung carcinoma: Recently, four major subtypes have been identified based on the expression of the transcription factors achaete-scute homologue 1 (ASCL1, SCLC-A subtype), neurogenic differentiation factor 1 (NEUROD1, SCLC-N subtype), POU class 2 homeobox 3 (POU2F3, SCLC-P subtype), and yes-associated protein 1 (YAP1, SCLC-Y subtype) [6].