11C-acetate PET/CT for metabolic characterization of multiple myeloma: a comparative study with 18F-FDG PET/CT.

We prospectively compared (11)C-acetate with (18)F-FDG in a PET/CT evaluation of multiple myeloma (MM), specifically on diagnostic accuracy, identification of high-risk patients, and monitoring of treatment response. Dual-tracer PET/CT was performed on 35 pathologically and clinically confirmed and untreated patients (26 with symptomatic MM, 5 with smoldering MM, and 4 with monoclonal gammopathy of unknown significance) and 20 individuals with normal marrow. (11)C-acetate showed significant incremental value over (18)F-FDG (84.6% vs. 57.7%) for positively identifying patients with diffuse and focal symptomatic MM, and was negative in patients with indolent smoldering MM and monoclonal gammopathy of unknown significance. Three functional parameters-number of (11)C-acetate-avid and (18)F-FDG-avid focal bone lesions and (11)C-acetate general marrow activity-strongly correlated with β-2-microglobulin as surrogate imaging markers of tumor burden. After induction chemotherapy, the metabolic change in (11)C-acetate general marrow activity correlated with clinical response. Metabolic characterization of MM in diagnosis, risk stratification, and treatment monitoring can be done more accurately by assessing lipid metabolism with (11)C-acetate than by assessing glucose metabolism with (18)F-FDG.