POU2F3 and small cell lung carcinoma: In 2019, Rudin et al. introduced a novel model of SCLC subtypes—A, N, P, and Y—defined by differential expression of four key transcription regulators: achaete-scute homologue 1 (ASCL1), neurogenic differentiation factor 1 (NEUROD1), POU class 2 homeobox 3 (POU2F3), and yes associated protein 1 (YAP1) [107, 108].