Prognostic Value of Very Early Interim FDG PET/CT After Single Cycle of Chemotherapy for 10-Year Survival in Diffuse Large B-Cell Lymphoma

Background/Objectives This study aimed to evaluate whether very early interim ¹⁸F-fluoro-2-deoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) after a single cycle of first-line chemotherapy predicts long-term survival outcome in patients with diffuse large B-cell lymphoma (DLBCL). Methods A total of 51 patients (31 males and 20 females; mean age 55 years) had four FDG PET/CT studies, at baseline and after one, three, and six cycles of chemotherapy (PET0, PET1, PET3, and PET6). Visually and quantitatively assessed PET parameters were analyzed for associations with long-term survival. Results The estimated 10-year progression-free survival (PFS) and overall survival (OS) was 48% and 61%, respectively. During a median follow-up of 63 months (range 9-134), 17 patients (33%) exhibited disease progression and 15 (29%) died. On PET1, all but one showed decreased FDG uptake, and all showed decreased metabolic tumor volume. None of the PET1 or PET3 parameters were associated with survival. The PET6 parameters retained independent predictive value for OS after adjustment for the International Prognostic Index. Negative PET6 was associated with longer PFS (mean 99 vs. 50 mo, <i>p</i> = 0.04) and OS (mean 107 vs. 57 mo, <i>p</i> = 0.02). Con-clusions The FDG PET/CT parameters obtained after a single cycle of chemotherapy were not associated with long-term survival in DLBCL, while negative end-of-therapy FDG PET/CT was associated with longer PFS and OS. Tumor regression very early into first-line chemotherapy was not as clinically relevant as the presence of viable tumor on FDG PET/CT at the end of therapy for predicting long-term outcomes.