Internal medicine
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Immune checkpoint inhibitors (ICIs) can cause immune-related adverse events (irAEs). There are a few case reports of remitting seronegative symmetrical synovitis with pitting edema syndrome (RS3PE) as an irAE. ⋯ The patient's lung cancer was in complete remission, leading to the diagnosis of RS3PE induced by pembrolizumab rather than malignancy. When patients show RS3PE during ICI treatment, rheumatologists should consider the possibility of an irAE after excluding malignancy and systemic diseases.