NEUROD1 and small cell lung carcinoma: SCLC subtypes were characterized based on mRNA expression profiles defined by the differential expression of three key transcription regulators, achaete-scute homologue 1 (ASCL1; also known as ASH1), neurogenic differentiation factor 1 (NeuroD1), and POU class 2 homeobox 3 (POU2F3), and low expression of all three transcription factor signatures accompanied by an inflamed gene signature (SCLC-A, N, P, and I, respectively)9.