Purpose: 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.
Patients and methods: 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.
Results: 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).
Conclusion: 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.