POU3F2 and small cell lung carcinoma: These subtypes are defined primarily by master transcriptional regulators (lineage factors): achaete-scute homolog 1 like (ASCL1), neurogenic differentiation factor 1 (NEUROD1), and POU class 2 homeobox 3 (POU2F3), with ASCL1-dominant SCLC representing the most common SCLC type (~70% of cases)63,64.