YAP1 and small cell lung carcinoma: This has led to a transcription factor-based classification, identifying four core SCLC subtypes based on the expression of lineage-defining transcription factors (TFs): ASCL1 (SCLC-A), NEUROD1 (SCLC-N), POU2F3 (SCLC-P), and YAP1 (SCLC-Y) [14] (Figure 1A,B).