ASCL1 and neoplasm: However, multi-omic approaches to SCLC profiling have now enhanced our understanding of the tumor highlighted by a model of four distinct subtypes characterized by the relative expression of key transcriptional factors: achaete-scute homolog 1 (ASCL1), neurogenic differentiation factor 1 (NeuroD1), and POU class 2 homeobox 3 (POU2F3), corresponding to subtypes SCLC-A (ASCL1 dominant), SCLC-N (NeuroD1 dominant), and SCLC-P (POU2F3 dominant), respectively.