Since the approval of pembrolizumab anti-PD-1 immunotherapy by the Food and Drug Administration in 2017 for the treatment of unresectable or metastatic, MSI-high/dMMR tumors, irrespective of the site of organ and histological subtype and irrespective of PDL-1 testing, detection of dMMR/MSI is considered a crucial tool for determining the therapy for many cancers. The gene discussed is CD274; the disease is cancer.