Predictive Value of Interim and End-of-Therapy 18F-FDG PET/CT in Patients with Follicular Lymphoma

Purpose: ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) is the standard imaging modality for response evaluation in FDG-avid lymphoma, but the prognostic value is not established in follicular lymphoma (FL). This study investigated the prognostic value of Deauville 5-point scale (D5PS) from paired interim PET/CT (PET_Interim) and end-of-induction therapy PET/CT (PET_EOI) in patients with FL.

Methods: FL staging and response assessment PET/CT images from 2013 to 2015 were retrospectively reviewed. PET_Interim was performed 3 or 4 cycles after chemotherapy and PET_EOI after 6 or 8 cycles. D5PS scores of 1, 2, and 3 were considered as negative (-), and scores 4 and 5 were considered as positive (+). Statistical analysis was done using Cox regression analysis, Kaplan-Meier survival analysis, and the log-rank test.

Results: Thirty-three patients with set of baseline, interim, and end-of-induction therapy PET/CT studies were included. Ten patients (30.3%) had progression. The median progression-free survival (PFS) was 38.8 months (range 3.5-72.7 months). On PET_Interim, 23 patients were negative and 10 were positive. On PET_EOI scans, 29 patients were negative, and 4 were positive. On multivariate analysis, PET_EOI(-) was associated with longer PFS. PET_Interim(+) and PET_EOI(+) patients had a significantly shorter PFS than PET_Interim(-) patients (39.9 months, 95% confidence interval [CI] 23.0-56.9, versus 55.5 months, 95% CI 49.7-61.2, p = 0.005) and PET_EOI(-) patients (14.2 months, 95% CI 8.5-19.8, versus 60.5 months, 95% CI 52.1-69.0, p < 0.001).

Conclusion: For patients with FL, PET_Interim and PET_EOI response is predictive of PFS, and PET_EOI(+) is an independent prognostic factor for progression of FL.