ASCL1 and small cell lung carcinoma: As a result of such studies, recent consensus suggested grouping SCLC into four subtypes defined by mRNA expression of ASCL1, NEUROD1, POU2F3, and YAP1. Consequently, a working nomenclature for SCLC subtypes defined by the relative expression of these four factors was proposed, classifying cases as: ASCL1 high (SCLC-A), NEUROD1 high (SCLC-N), POU2F3 high (SCLC-P), and YAP1 high (SCLC-Y) [12,59,60,61].