Purpose: Response evaluation with conventional criteria based on computed tomography (CT) is particularly challenging in malignant pleural mesothelioma (MPM) due to its diffuse pattern of growth. There is growing evidence that therapy-induced changes in tumor [(18)F]fluorodeoxyglucose (FDG) uptake as measured by positron emission tomography (PET) may predict response and patient outcome early in the course of treatment.
Patients and methods: Patients with histologically proven MPM, not candidates to curative surgery, scheduled to undergo palliative chemotherapy with a pemetrexed-based regimen were eligible for this study. Patients were evaluated by FDG-PET and CT at baseline and after two cycles of therapy. A decrease of 25% or more in tumor FDG uptake as measured by standardized uptake value was defined as a metabolic response (MR). Best overall response from CT scans was determined according to previously published criteria.
Results: Twenty-two patients were included in the study, and 20 were assessable for early metabolic response with FDG-PET. Of these, eight were classified as responders (40%) and 12 as nonresponders (60%). Early MR was significantly correlated to median time-to-tumor progression (TTP) with a median TTP for metabolic responders of 14 months versus 7 months for nonresponders (P = .02). No correlation was found between TTP and radiologic response evaluated by CT. Patients with a MR had a trend toward longer overall survival.
Conclusion: The use of MR evaluated by FDG-PET in the assessment of treatment efficacy in MPM appears promising. Our observations need to be validated in a larger prospective series.