MRC1 and hyperinsulinemic hypoglycemia, familial, 4: Previous studies reported that patients with MMR deficiency showed a good response to PD-1 blockade for solid tumours, including GC.15,16,20 Therefore, pembrolizumab received approval by the US Food and Drug Administration in May 2017 for the treatment of patients with MSI-high or MMR-deficient solid tumours.