Cancer Treatment Response to Checkpoint Inhibitors Is Associated with Cytomegalovirus Infection

Programmed cell death protein-1 (PD-1) and programmed cell death-ligand 1 (PD-L1) checkpoint inhibitors induce tumor response by activating the patient’s own immune system to fight cancer. Tumors with high tumor mutational burden or those that express high levels of PD-1/PD-L1 are more responsive to PD1/PDL1 inhibitors. There is much interest in determining how to improve response to PD-1/PD-L1 inhibitors. We report a case of a patient with metastatic bladder cancer who was primarily resistant to treatment with PD-1/PD-L1 inhibitors, then had a complete response after developing cytomegalovirus infection.