Metabolic Tumor Volume assessed by 18F-FDG-PET/CT in the evaluation of plasma cell mass and prediction of outcome in patients with multiple myeloma

In multiple myeloma, the amount of plasma cells infiltrating the bone marrow and haemoglobin levels are considered two of the most important clinical and haematological parameters indicating the clinical status of disease. 18F-FDG-PET/TC allows the direct measurement of metabolic tumor burden thus reflecting plasma cell mass and providing potential informations about prognosis of myeloma patients. Aim. To assess whether metabolic tumor volume (MTV) determined by whole-body 18F-FDG-PET/CT correlates with haematological variables and if it can be of use in the prediction of overall survival in multiple myeloma patients. Materials and Methods. Forty-one patients (16 females, 25 males; mean age±SD 63±11) with stage IIIA multiple myeloma underwent whole-body 18F-FDG-PET/CT. Imaging data were transferred to a xeleris workstation in DICOM format and 3D region of interest analysis was performed on PET images 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 41 patients studied, MTV ranged from 1.3 to 316,3 ml with a median value of 23.7 ml. Patients who died at follow-up (n=7) had a significantly higher MTV (100±64 ml vs 35±55 ml, p<0.01) than patients that were still alive (n=34). Overall survival was significantly better in patients with MTV <=23.7 ml as compared to those having MTV >23.7 (95% vs 70%, p<0.01). No differences in age, performance status and therapeutic regimen were found between the two groups. A direct and significant correlation was found between MTV values and the percentage of infiltrating plasma cells (r=0.45, p<0.05) whereas haemoglobin levels were inversely and significantly correlated with MTV (r=-0.54, p<0.001). Conclusion. The direct measurement of tumor burden obtained by calculating the MTV value on 18F-FDG-PET/CT images reflects plasma cell mass and may be used in the prediction of overall survival in multiple myeloma patients.