ASCL1 and small cell lung carcinoma: The new SCLC molecular subtypes are defined by the relative expression levels of four key transcription factors: achaete-scute homologue 1 (ASCL1), neurogenic differentiation factor 1 (NEUROD1), yes-associated protein 1 (YAP1), and POU class 2 homeobox 3 (POU2F3) [15].