CD274 and hyperinsulinemic hypoglycemia, familial, 4: Given that mismatch repair (MMR) deficiency and programmed cell death-ligand 1 (PD-L1) expression serve as important biomarkers for immunotherapy response, with positive predictive values reported in multiple solid tumors, studies have shown that MMR deficiency occurs in approximately 2–3% of ovarian cancers and is associated with increased tumor mutational burden and enhanced response to immunotherapy [11].