Relevance of monitoring metabolic reduction in patients with relapsed or refractory follicular and mantle cell lymphoma receiving bendamustine: A multicenter study

The aim of the present study was to investigate the relevance of monitoring metabolic reduction evaluated by ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET/CT in relapsed or refractory patients with follicular lymphoma (FL) and mantle cell lymphoma (MCL) who received bendamustine. We conducted a phantom study of 18F-FDG PET/CT to ensure quality control for performing a multicenter clinical study. We analyzed 49 patients with relapsed or refractory FL and MCL who received bendamustine (120mg/m²) on days 1-2 of a 21-day cycle for up to six cycles as a licensing phase II study. 18F-FDG PET/CT scans were acquired before the first and after the last cycle. In a total of 175 target lesions, the maximum perpendicular diameter (Max PD), minimum PD (Min PD), sum of the products of the Max PD (SPD), maximum standardized uptake value (SUVmax), and the percentage reduction rates of Max PD (%Max PD), SPD (%SPD) and SUVmax (%SUVmax) were evaluated for the response to treatment. The therapeutic response was assessed after the last cycle of treatment according to the revised response criteria for malignant lymphoma (revised RC). We evaluated 134 lesions in 39 patients (76%) achieving complete response (CR) and 41 lesions in 10 patients (24%) not achieving CR. The Max PD, Min PD, SPD and SUVmax of the lesions after the last cycle were significantly higher in patients with non-CR than in patients with CR. The %MPD, %SPD and %SUVmax of the lesions were significantly greater in patients with CR than in patients with non-CR (P<0.0001). Metabolic reduction was observed in all target lesions of relapsed or refractory patients with FL and MCL who achieved CR after bendamustine therapy.