Biomarkers, like PD-L1 expression, tumor mutational burden(TMB), DNA mismatch repair deficiency (dMMR), and tumor-infiltrating lymphocytes (TILs), have been utilized to select patients responsive to PD-1/PD-L1inhibitors in the clinic, but each of them has limited use. The gene discussed is PDCD1; the disease is hyperinsulinemic hypoglycemia, familial, 4.