Abstract
Immune checkpoint inhibitors (ICIs) are monoclonal antibodies that target T lymphocytes and stimulate the immune system. However, the use of ICIs is associated with immune-related adverse events (irAEs). Pericardial disease is a cardiovascular irAEs that can present as cardiac tamponade. The precise mechanisms underlying pericardial complications are not fully understood. Late-onset hemorrhagic pericardial effusion associated with ICIs is quite rare; the mechanism and predisposing factors are yet to be determined. This case report describes a patient with diffuse large B-cell lymphoma (DLBCL) who received pembrolizumab for 390 days and subsequently developed cardiac tamponade caused by hemorrhagic pericardial effusion. The purpose of this report is to raise awareness about the occurrence of late-onset cardiac tamponade and provide a summary of available data on patients who experienced hemorrhagic pericardial effusion during ICI treatment.