ASCL1 and small cell lung carcinoma: To improve the treatment outcomes of ES-SCLC, Rudin et al. recently defined four major subtypes of SCLC based on the expression of the following key transcription factors: achaete-scute homolog 1 (ASCL1), neurogenic differentiation factor 1 (NEUROD1), yes-associated protein 1 (YAP1) and POU class 2 homeobox 3 (POU2F3), which correspond to the SCLC-A (ASCL1-dominant), SCLC-N (NEUROD1-dominant), SCLC-P (POU2F3-dominant) and SCLC-Y (YAP1-dominant) molecular subtypes, respectively [69].