NEUROD1 and small cell lung carcinoma: Recently, extending the concepts of classic and variant SCLC, both intertumoral, and intratumoral heterogeneity in SCLC has been documented and has been associated with the expression of lineage-specific transcription factors (TFs) ASCL1, NEUROD1, YAP1, and POU2F3, and these various subtypes express different levels of NE markers19–21.