Pembrolizumab was the first PD-L1/PD-1 blocking agent to be approved by the FDA, being granted the designation of breakthrough therapy for malignant melanoma in 2014.8 Other PD-L1/PD-1 blocking antibodies, including nivolumab, atezolizumab, durvalumab and avelumab, have been approved for clinical use.9–13 In 2017, pembrolizumab was the first FDA-approved immunotherapeutic agent for the treatment of solid tumors with unresectable mismatch-repair deficiency and microsatellite instability.14 The gene discussed is CD274; the disease is melanoma.