ASCL1 and small cell lung carcinoma: In 2019, SCLC molecular subtypes were defined based on expression of master neurogenic transcription factors (TFs) ASCL1 (SCLC-A) and NEUROD1 (SCLC-N) and a rarer subtype defined by the non-NE tuft cell TF POU2F3 (SCLC-P).11