UCLA Department of Medicine Clinical Insights

Immune checkpoint inhibitors have transformed the treatment of advanced malignancies, but their capacity to amplify immune activity extends beyond tumor cells, producing a spectrum of immune-related adverse events that increasingly bring patients to rheumatology clinics. Inflammatory arthritis is among the most common rheumatologic manifestations, occurring in roughly 4–6% of patients, and may present as seronegative symmetric polyarthritis, oligoarthritis, or polymyalgia rheumatica–like disease. This essay reflects on a clinical encounter with an older woman receiving checkpoint inhibitor therapy for metastatic melanoma who developed functionally limiting inflammatory arthritis at the very moment her cancer treatment appeared to be working. Her experience illuminates the central paradox of immunotherapy: the mechanism that enables tumor destruction can simultaneously turn against the patient’s own tissues. Through this encounter, the essay explores the clinical features, pathophysiology, and management of checkpoint inhibitor–associated arthritis, and reflects on the broader challenge of helping patients navigate the sustained tension between a therapy that is both healing and causing harm. The role of the rheumatologist in this era extends beyond suppressing inflammation—it includes bearing witness to the complexity that modern oncology has introduced into patients’ lives.