Pembrolizumab (Keytruda), a monoclonal antibody that inhibits the action between PD-1 and PD-L1 and PD-L2, is approved by the US Food and Drug Administration (FDA) for patients with metastatic non–small cell lung cancer (NSCLC) whose tumors express PD-L1, as determined by an FDA-approved test. Here, PDCD1LG2 is linked to non-small cell lung carcinoma.