In May 2017, the FDA granted accelerated approval to the anti-PD-1 mAb pembrolizumab for the treatment of adult and pediatric patients with unresectable or metastatic microsatellite instability-high (MSI-H) or mismatch repair-deficient (dMMR) solid tumors that continued to progress after conventional treatment, based on the data from 149 patients with MSI-H or dMMR cancers enrolled across 5 clinical trials: KEYNOTE-016, KEYNOTE-164, KEYNOTE-012, KEYNOTE-028, and KEYNOTE-158 [2]. The gene discussed is PDCD1; the disease is cancer.