RB1 and small cell lung carcinoma: Homologous recombination repair (HRR)-deficient tumors result in a higher tumor mutational load, including KEAP1-mutated non-small cell lung cancer (NSCLC) (92), BRCA1/2-deficient tumors (93, 94), microsatellite instability (MSI) colorectal cancer (CRC) (95), and small cell lung cancer (SCLC) (66) characterized by widespread deletion of two key regulators of the cell cycle checkpoint pathway, TP53 and RB1.