Combined FDG-PET/CT in response evaluation of malignant pleural mesothelioma

Based on the complex growth pattern of MPM, conventional response evaluation in this cancer entity is challenging. Therefore, there is growing interest in therapy response evaluation with FDG-PET/CT. The aim of the study was to evaluate the value of several FDG-PET/CT-parameters in therapy response evaluation concerning prediction of survival at baseline and after three cycles of therapy.

The study was performed in accordance with the regulations of the local ethics committee. Forty-one patients with proven MPM and treated with palliative pemetrexed and platinum-based chemotherapy were included. All patients were evaluated by FDG-PET/CT at baseline and after three cycles of chemotherapy. Responders and non-responders were evaluated based on modified RECIST- and EORTC-criteria. Additional PET-parameters (SUVmean, tumor lesion glycolysis (TLG) and tumor volume (PETvol)) were evaluated. Results were evaluated using the COX regression and the Kaplan-Meier method.

None of the baseline CT-measurements or the initial PET-parameters were predictive for survival. Based on CT, after three cycles of therapy 10 patients were categorized as responders, 30 were classified as stable disease and 1 had progressive disease. Based on PET-evaluation, 14 responders were identified, 23 patients with stable disease and 4 patients were progressive. CT-response after 3 cycles of chemotherapy was significantly related to overall survival (p=0.001). However, neither SUVmax-response (p=0.61) nor SUVmean-response (p=0.68) were related to survival. A decrease of TLG and PETvol, however, was found to be predictive (TLG: p=0.01; PETvol: p=0.002).

Response evaluation based on modified RECIST by CT as well as response evaluation by TLG and PETvol in FDG-PET, but not SUVmax-measurements are predictive for survival in MPM.