ASCL1 and small cell lung carcinoma: initially classified SCLC into four transcriptional subtypes based on the expression of key transcription factors, achaete-scute homolog 1 (ASCL1), neurogenic differentiation factor 1 (NEUROD1), POU class 2 homeobox 3 (POU2F3), and YAP1, using RNA-seq data (98).