Researchers observed a prevalence of malignancy in patients with immunoglobulin G4-related disease (IgG4-RD) that was 2.5 times higher than expected from the Surveillance, Epidemiology, and End Results (SEER) database. In addition, compared with the rate for matched controls, a history of cancer was 3.5 times higher in IgG4-RD patients. Possible explanations include possible shared risk factors for IgG4-RD and cancer, as well as cancer’s triggering of autoantigen expression leading to IgG4-RD.