NEUROD1 and neoplasm: SCLC is a neuroendocrine (NE) tumor (Travis et al., 2015), and recent studies have demonstrated that it is a molecularly heterogeneous disease comprising discrete tumor subtypes defined by expression of different transcriptional regulators, namely achaete-scute homolog 1 (ASCL1) and neurogenic differentiation factor 1 (NEUROD1), which together account for approximately 80% of SCLC cases (Borromeo et al., 2016; Rudin et al., 2019).