In addition to the unique sample cohort, our study presents two aspects of the ITH of SCLC: 1) the heterogeneous expression in malignant cells of genes related to the cell cycle, immunity, hypoxia, EMT, and other hallmarks; 2) the heterogeneous expression of key TFs of SCLC, most commonly ASCL1 and NEUROD1. These results markedly enhanced our understanding of the clinical features of SCLC. This evidence concerns the gene NEUROD1 and small cell lung carcinoma.