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. Here, CD274 is linked to small cell lung carcinoma.