ASCL1 and small cell lung carcinoma: SCLC-A is characterized by high achaete-scute homolog 1 (ASCL1) expression; SCLC-N is defined by neurogenic differentiation factor 1 (NEUROD1) expression; SCLC-P is characterized by upregulated POU domain, class 2, transcription factor 3 (POU2F3) expression; and SCLC-Y is characterized by expression of the Yes-associated protein 1 (YAP1)15.