Metabolic tumor volume assessed by 18F-FDG-PET/CT for the prediction of outcome in patients with multiple myeloma

18F-FDG-PET/CT allows the direct measurement of metabolic tumor burden in a variety of different malignancies. Aim. To assess whether metabolic tumor volume (MTV) determined by 18F-FDG-PET/CT can be used in the prediction of progression-free and overall survival in multiple myeloma patients. Methods. Forty-seven patients (18 females, 29 males; mean age 63±11 y) with stage IIIA disease underwent whole-body 18F-FDG-PET/CT. Images were subjected to a 3D region of interest analysis taking into account all focal lesions with an SUVmax>2.5. MTV of each lesion was calculated using an in-house developed SUV-based automated contouring program that uses a threshold of 40% of the SUVmax. The total MTV of each patient was defined as the sum of metabolic volume of all focal lesions. Patients were treated and then subjected to a mean follow-up period of 24 months. Results. In the 47 patients studied, MTV ranged from 1.3 to 316.3 ml with a median value of 23.7 ml. A direct and significant correlation was found between MTV and percentage of infiltrating plasma cells (r=0.46, p=0.006) whereas haemoglobin levels were inversely and significantly correlated with MTV (r=-0.56, p=0.0001). At follow-up, patients who developed progressive disease (n=18) showed a significantly higher MTV (74.7±19.3 ml vs 29.8±5.1 ml, p=0.009) than patients without progression (n=29). Furthermore patients who died of myeloma (n=9) had a significantly higher MTV (123.2±30.6 ml vs 28.9±4.2 ml, p=0.0001) than survivors (n=38). No differences in age, plasma cell infiltration, monoclonal component, albumin, β2-microglobulin, performance status, ISS stage and presence or absence of bone marrow transplant were found between groups. MTV cut-off level was determined by ROC curve analysis and the best discriminative value found for predicting progression-free and overall survival was 42.2 ml and 77.6 ml, respectively. By Kaplan-Meier analysis and log-rank test, progression-free and overall survival at follow-up were significantly better in patients showing MTV lower than the cut-off level as compared to those having MTV higher than the cut-off (χ2=3.9, p=0.04 and χ2=56.3, p<0.0001, respectively). Conclusion. The direct measurement of tumor burden obtained by calculating MTV 1on 18F-FDG-PET/CT images may be used in the prediction of progression-free and overall survival in myeloma patients.