Prognostic value of very early interim FDG PET/CT after single cycle of chemotherapy for 10-year survival in diffuse large B-cell lymphoma

Introduction: This study aimed to evaluate whether very early interim 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) after single cycle of chemotherapy predicts long term survival outcome in patients with diffuse large B-cell lymphoma (DLBCL).

Methods: We prospectively enrolled patients with histologically confirmed DLBCL. All patients received standard first-line chemotherapy and had four FDG PET/CT studies using same protocol and system: at baseline and after one (PET1), three, and six cycles of chemotherapy (PET6). FDG PET/CT images were assessed visually using the Deauville 5-point scale and quantitatively using peak standardized uptake value normalized by lean body mass (SULpeak) and metabolic tumor volume (MTV). The associations between FDG PET/CT findings and survival were statistically assessed.

Results: A total of 51 patients (31 males and 20 females; mean age 55 years) were included in this study. During a median follow-up of 63 months (range 9–134), 17 patients (33%) exhibited disease progression and 15 (29%) died of any cause. The estimated 10-year progression-free survival (PFS) and overall survival (OS) were 48% and 61%, respectively. On PET1, all but one patient showed decreased SULpeak (mean 74%, range -47–96%) and all patients showed markedly decreased MTV (mean 94%, range 18–100%). In univariate analysis, none of PET1 parameters were significantly associated with survival. Of PET6 parameters, Deauville score, SULpeak, MTV, and percent change of MTV were significantly associated with PFS and OS and percent change of SULpeak was significantly associated with OS. All five PET6 parameters retained independent predictors of OS after adjustment for International Prognostic Index. The Deauville score of 1, 2, or 3 at PET6 predicted longer PFS (mean 99 versus 50 months, p=0.038) and OS (mean 107 versus 57 months, p=0.02).

Conclusions: FDG PET parameters obtained very early after single cycle of first-line chemotherapy were not associated with long term survival outcome in patients with DLBCL. On the other hand, negative end-of-therapy FDG PET performed after six cycles was significantly associated with longer PFS and OS. The rate of tumor regression very early into first-line chemotherapy was not as clinically relevant as presence of viable tumor at end-of-therapy for long term outcome.