Interestingly, Shirasawa proposed a pathological classification of SCLC on the basis of IHC evaluation of ASCL1, NEUROD1, POU2F3, and YAP1 expression: pathological SCLC-A (pSCLC-A), pSCLC-N, pSCLC-P, and pSCLC-Y. This evidence concerns the gene ASCL1 and small cell lung carcinoma.