POU2F3 and small cell lung carcinoma: In the past 5 years, there have been substantial developments in identifying distinct molecular subtypes of SCLC based on differential expression of transcription factor genes (ASCL1, NEUROD1, POU2F3 – respectively, SCLC-A, SCLC-N, and SCLC-P subtypes) or low/lack of expression of these genes.