Quantitative analyses at baseline and interim PET evaluation for response assessment and outcome definition in patients with malignant pleural mesothelioma

Purpose Quantitative analyses on FDG PET for response assessment are increasingly used in clinical studies, particularly with respect to tumours in which radiological assessment is challenging and complete metabolic response is rarely achieved after treatment. A typical example is malignant pleural mesothelioma (MPM), an aggressive tumour originating from mesothelial cells of the pleura. We present our results concerning the use of semiquantitative and quantitative parameters, evaluated at the baseline and interim PET examinations, for the prediction of treatment response and disease outcome in patients with MPM. Methods We retrospectively analysed data derived from 131 patients (88 men, 43 women; mean age 66 years) with MPM who were referred to our institution for treatment between May 2004 and July 2013. Patients were investigated using FDG PET at baseline and after two cycles of pemetrexed-based chemotherapy. Responses were determined using modified RECIST criteria based on the best CT response after treatment. Disease control rate, progression-free survival (PFS) and overall survival (OS) were calculated for the whole population and were correlated with semiquantitative and quantitative parameters evaluated at the baseline and interim PET examinations; these included SUVmax, total lesion glycolysis (TLG), percentage change in SUVmax (Delta SUVmax) and percentage change in TLG (Delta TLG). Results Disease control was achieved in 84.7 % of the patients, and median PFS and OS for the entire cohort were 7.2 and 14.3 months, respectively. The log-rank test showed a statistically significant difference in PFS between patients with radiological progression and those with partial response (PR) or stable disease (SD) (1.8 vs. 8.6 months, p<0.001). Baseline SUVmax and TLG showed a statistically significant correlation with PFS and OS (p<0.001). In the entire population, both Delta SUVmax and Delta TLG were correlated with disease control based on best CT response (p<0.001). Delta SUVmax was significantly correlated with PFS in the entire population (p=0.02) and with both PFS and OS in patients not undergoing talc pleurodesis (n=65; p<0.01 for PFS, p=0.03 for OS), and in patients without pleurodesis presenting a SD and/or PR at CT after two cycles. Conclusion These results confirm the role of FDG PET in the assessment of disease prognosis and treatment efficacy in MPM patients receiving first-line pemetrexed-based chemotherapy. In particular, metabolic response evaluated using Delta SUVmax can be used to predict outcome in MPM patients not undergoing talc pleurodesis who achieve SD and/or PR at the interim CT evaluation.