A phase 2 study evaluated the clinical activity of pembrolizumab, a humanized immunoglobulin G4 (IgG4) κ anti-PD1 mAb, against programmed cell death protein 1 (PD-1) in 41 patients with advanced metastatic carcinoma with or without mismatch repair deficiency, a number of them having cholangiocarcinoma [133]. The gene discussed is PDCD1; the disease is hyperinsulinemic hypoglycemia, familial, 4.