False Suggestion of Malignant Transformation of Benign Bone Tumor by 18F-FDG PET/CT

A 68-year-old man underwent serial F-FDG PET/CT scan follow-up for lung cancer. Then 5.5 years after the initial F-FDG PET/CT scan, the presumed benign bone tumor in the left clavicle showed markedly increased FDG uptake during follow-up; in contrast, the Tc-MDP bone scan paradoxically exhibited no apparent interval change since last bone scan 5.5 years earlier. He underwent a CT-guided biopsy, and the pathological diagnosis was benign fibrous histiocytoma. The result was consistent with the lack of progression in Tc-MDP bone scan, whereas the F-FDG PET/CT scan gave a false-positive impression of malignant transformation.