Interim FDG PET/CT as a prognostic factor in diffuse large B-cell lymphoma

Interim F-18-FDG PET performed early during the course of therapy in diffuse large B-cell lymphoma (DLBCL) is a good predictor of outcome. However, interpretation criteria for interim PET for the evaluation of tumour response are still not clearly defined. The study aim was to assess whether interim PET can predict overall survival (OS) and progression-free survival (PFS) in DLBCL patients following three different sets of parameters, two qualitative (visual) methods and one semiquantitative. A total of 50 newly diagnosed DLBCL patients were prospectively enrolled in this study. All patients had a PET/CT scan at diagnosis and an interim PET/CT scan after the second or third cycle of chemotherapy. Three methods of evaluation for the interim PET/CT were used: a qualitative three-point scoring (3-PS) method, a qualitative 5-PS method and a semiquantitative method (Delta SUVmax). The degree of correlation between therapy response seen on FDG PET and PFS and OS was determined. The analysis of the visual 3-PS method showed no statistically significant difference in PFS and OS. The estimated 5-year PFS and OS were 79 % and 92 %, respectively, in patients with an interim PET scan showing uptake not greater than in the liver versus 50 % in patients with uptake greater than in the liver, and this difference was statistically significant. The optimal cut-off value of Delta SUVmax that could predict the PFS and OS difference in patients with DLBCL was 76 % (95 % CI 62.7-89.2 %) and 75 % (95 % CI, 54.6-95.4 %), respectively. Our results support the use of liver uptake as an indicator in the qualitative evaluation of interim PET, or a Delta SUVmax greater than 75 % in semiquantitative analysis. Interim PET may predict PFS and OS and could be considered in the prognostic evaluation of DLBCL.