Predictive role of FDG PET-derived parameters on outcome after salvage radiotherapy in progressive malignant pleural mesothelioma

Objectives: Malignant pleural mesothelioma (MPM) has an aggressive course, high mortality rate and no standard of care. Aim of the current study was to evaluate the predictive role of FDG PET-derived parameters in MPM patients treated with salvage helical tomotherapy (HTT) on overall survival (OS), local relapse free survival (LRFS) and distant relapse free survival (DRFS).

Methods: Fifty-five MPM patients (44 male and 11 female) with a median age of 67 years (range: 39-82 years), treated between March 2006 and February 2015 at San Raffaele Scientific Institute were retrospectively investigated. The patients were treated with FDG PET/CT guided salvage HTT after previous surgery plus chemotherapy. Univariate Cox regression analysis was performed to assess the impact of several quantitative FDG PET-derived parameters: biological target volume (BTV), mean and maximum standard uptake value (SUVmean-max), metabolic tumour volume (MTV) and total lesion glycolysis (TLG), the last three parameters considered at different uptake threshold 40-50-60%. By considering patients with OS, LRFS and DRFS inferior and superior to the corresponding median time, a logistic regression was performed to select FDG PET-derived parameters able to better select patients with the worst prognosis.

Results: Median OS was 9.1 months (range: 0.0 - 69.6 months) after the end of HTT; 54/55 patients were dead at the last follow-up. BTV (p= 0.0007; RR= 1.0013) and TLG (p< 0.0001, RR= 1.001) were the most significant predictors of OS. The median values of MTV60 (p= 0.015; RR= 2.1) and TLG40-50 (p= 0.0047; RR= 2.4) significantly predict OS; a median OS equal to 4.8 months was found for patients with MTV60> 5.0 cc and for TLG40> 334.4 cc compared to 13.8/16.1 months, respectively for patients with smaller MTV60 and TLG40. Median LRFS and DRFS were 6.2 months (range: 1.2 - 39.4 months) and 6.5 months (0.0 - 66.4 months), respectively. TLG40-50-60 were found significantly (p< 0.015) correlated to LRFS. Almost all FDG PET-derived parameters were found significantly correlated with DRFS. In particular, a median DRFS equal to 6.4 /6.2 months was found for patients with a MTV40> 39.6 cc /TLG40> 334.4 cc compared to 17.0/18.8 months for patients with MTV40 and TLG40 smaller than these values. FDG PET-derived parameters well discriminated patients with poor OS/LRFS/DRFS (less than the median values): BTV (p= 0.0044; RR= 5.8); BTV(p= 0.055; RR= 3) and TLG40 (p= 0.039; RR= 3.4); MTV40 (p= 0.0036; RR= 6.5), MTV60 and TLG40-50 (p= 0.0018; RR= 7.6) were the best parameters for OS, LRFS and DRFS, respectively.

Conclusion: FDG PET-derived parameters predict outcome of MPM patients treated with salvage HTT. The predictive value of PET-derived parameters may be helpful in identifying patients with the worst prognosis, potentially allowing a better selection of MPM patients for salvage HTT. Research Support: None