Owonikoko et al. showed four discrete subtypes of SCLC defined by variation in the expression levels of the transcription factors ASCL1 (SCLC-A), NEUROD1 (SCLC-N), POU2F3 (SCLC-P), and YAP1 (SCLC-Y) [129]. This evidence concerns the gene YAP1 and small cell lung carcinoma.