Fusion of metabolic function and morphology:: Sequential [18F] fluorodeoxyglucose positron-emission tomography/computed tomography studies yield new insights into the natural history of bone metastases in breast cancer

Purpose By monitoring bone metastases with sequential [F-18] fluorodeoxyglucose positron-emission tomography/ computed tomography ([F-18] FDG-PET/CT) imaging, this study investigates the clinical relevance of [F-18] FDG uptake features of bone metastases with various radiographic appearances. Patients and Methods Bone metastases were found in 67 of 408 consecutive patients with known/ suspected recurrent breast cancer on [F-18] FDG- PET/CT, characterized by CT morphology changes and/ or bony [F-18] FDG uptake. Twenty-five of the patients had sequential [F-18] FDG- PET/ CT examinations ( 86 studies) over an average follow- up period of 23 months. The temporal changes in [F-18] FDG uptake and corresponding CT morphology features of 146 bone lesions identified in these 25 patients were followed up and correlated with therapeutic outcome retrospectively. Results The 146 lesions were classified as osteolytic (77), osteoblastic (41), mixed-pattern (11), or no change/ negative ( 17) on CT. The majority of the osteolytic (72; 93.5%) and mixed- pattern lesions ( nine; 81.8%), but fewer of the osteoblastic lesions (25; 61%), showed increased [F-18] FDG uptake. After treatment, 58 osteolytic lesions ( 0.5%) became [F-18] FDG negative and osteoblastic on CT and only 14 relatively large lesions (19.5%) remained [F-18] FDG avid. Of the 25 [F-18] FDG-avid osteoblastic lesions, 13 (52%) became [F-18] FDG negative, but 12 (48%) remained [F-18] FDG avid and increased in size on CT. Five of the mixed-pattern lesions remained [F-18] FDG avid after treatment. All 17 CT-negative lesions became [F-18] FDG negative; however, nine of them became osteoblastic. None of the initially [F-18] FDG-negative lesions showed [F-18] FDG avidity during follow-up. Conclusion [F-18] FDG uptake reflects the immediate tumor activity of bone metastases, whereas the radiographic morphology changes vary greatly with time among patients.