POU2F3 and small cell lung carcinoma: Three of the four subtypes are enriched in the predominant expression of specific transcription factors, ASCL1 (SCLC-A), NEUROD1 (SCLC-N), and POU2F3 (SCLC-P) while the fourth is an inflamed subtype (SCLC-I) associated with higher levels of PD-L1 and other checkpoint factors, and higher levels of interferon signaling and epithelial to mesenchymal transition (EMT) based on their transcriptomic signature 10.