Late-onset bone granulomatous reaction of hand from immune checkpoint-inhibitors detected on FDG-PET/CT

Immune checkpoint inhibitors (ICIs) enhance antitumor immunity by inhibiting intrinsic immune-suppressive pathways. Although immune-related adverse events (irAEs) typically arise in the early phase of ICI therapy, delayed manifestations have been reported, even months to years following treatment discontinuation. We report a case of a late-onset bone granulomatous reaction in the hand of a male patient in his seventies with a history of ICI therapy, identified on FDG-PET/CT, 4 years after discontinuation of ICI therapy. This case indicates the importance of recognizing the possibility of delayed irAEs, even in patients who have undergone long-term discontinuation of immunotherapy.