ASCL1 and small cell lung carcinoma: In addition to the unique molecular characteristics of SCLC, including the frequent loss of Rb and p531,4, SCLC can be categorized based on the expression of several key lineage-specific transcription factors (TFs), including ASCL1 (achaete-scute homolog 1; SCLC-A), NEUROD1 (neurogenic differentiation factor 1; SCLC-N), and POU2F3 (POU class 2 homeobox 3; SCLC-P), alongside other putative TFs, YAP1 (yes-associated protein 1; SCLC-Y)5,6 and ATOH1 (atonal basic helix-loop-helix [bHLH] transcription factor 1)7.