POU2F3 and small cell lung carcinoma: SCLC is classified into four main subgroups based on specific biomarkers or molecular factors (transcription factor-based): ASCL1 (SCLC-A), NEUROD1 (SCLC-N), POU2F3 (SCLC-P), and YAP1 (SCLC-Y) [29,30,31].