Pembrolizumab (Keytruda®) is a checkpoint inhibitor that targets the Programmed death-ligand 1 (PD-1/PD-L1) pathway; it has been approved for patients with advanced CC with high PD-L1 expression, high microsatellite instability (MSI-H), or high tumour mutational burden (TMB-H); and for patients with advanced OC with high microsatellite instability (MSI-H), DNA mismatch repair deficiency (dMMR), or high tumour mutational burden (TMB-H). The gene discussed is CD274; the disease is hyperinsulinemic hypoglycemia, familial, 4.