Immunotherapy has revolutionized the treatment of cancer, but a rapid rise in the use of the family of therapeutic agents known as checkpoint inhibitors (CPIs) is associated with a new group of immune-related adverse events (irAEs) in almost any organ system. Among these irAEs, rheumatic complications are common and seem to have features that are distinct from irAEs in other organ systems, including a highly variable time of clinical onset and the capacity to persist, possibly indefinitely, even after cessation of CPI therapy. In this Review, mechanisms of action of CPIs and how they might cause rheumatic irAEs are described. Also covered are epidemiology and clinical descriptions of rheumatic irAEs, plus guiding principles for managing irAEs. Finally, we outline future directions that must be taken in response to a series of unanswered questions and unmet needs that now confront rheumatologists who are, or will be, engaged in this new area of rheumatology.
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