In seminal findings by Rudin et al., SCLC subtypes were defined by the expression of four transcription factors: achaete-scute homologue 1 (ASCL1), neurogenic differentiation factor 1 (NEUROD1), yes-associated protein 1 (YAP1) and POU class 2 homeobox 3 (POU2F3) [128]. This evidence concerns the gene POU2F3 and small cell lung carcinoma.