NEUROD1 and small cell lung carcinoma: According to the differential expression levels of specific genes, SCLC subtypes are classified as follows: those with elevated achaete-scute homolog 1 (ASCL1) expression are designated SCLC-A; those with increased neurogenic differentiation factor 1 (NEUROD1) expression fall under SCLC-N; elevated POU class 2 homeobox 3 (POU2F3) expression delineates SCLC-P; and those with heightened yes-associated protein 1 (YAP1) expression are classified as SCLC-Y.