The recent molecular subclassification of SCLC into four subtypes, each characterized by the predominantly expression of a specific transcription factor, SCLC-A (ASCL1-driven), SCLC-N (NEUROD1-driven), SCLC-P (POU2F3-driven), and SCLC-I (inflamed or “triple-negative” subtype), offers a framework for understanding its heterogeneity and guiding subtype-specific therapeutic strategies. The gene discussed is ASCL1; the disease is small cell lung carcinoma.