TTF1 and small cell lung carcinoma: Similar to achaete‐scute homolog 1 (ASCL1, also known as ASH1), the NKX‐homeodomain family TFs play a critical role in reprogramming normal human epithelial tissues to a neuroendocrine cancer lineage (Park et al., 2018), suggesting a critical function of TTF‐1 in SCLC other than promoting epithelial cell differentiation.