FDG PET/CT predictive role in follicular lymphoma

Purpose We present findings concerning F-18-fluorodeoxyglucose (FDG) positron emission tomography (PET) at end-treatment evaluation in follicular lymphoma (FL) in order to establish possible predictive factors for progression-free survival (PFS) and patient outcome. Methods We retrospectively analysed data from 91 consecutive FL patients (M:F = 51:40, mean age 61) referred to our PET Unit at therapy completion: 38 with an indolent form (grade 1-2) and 53 with an aggressive FL (grade 3a and b) according to the World Health Organization (WHO) classification. A total of 148 FDG PET/CT scans were analysed and findings reported as positive or negative for disease. The overall response to treatment was assessed according to the revised International Workshop Criteria (IWC). The final outcome was defined as remission or disease by taking clinical, instrumental and histological data as standards of reference, with a mean follow-up period of 3 years (range 1-8). A statistical analysis was performed with respect to PFS and patient outcome for FDG PET result, tumour grading, Follicular Lymphoma International Prognostic Index (FLIPI), disease stage and number of relapses, on uni- and multivariate analyses, with p < 0.05 considered as significant. Results Overall patients presented a mean PFS of 35 months (range 3-86), with a relapse rate of 42%. At final outcome, remission was achieved in 67 of 91 patients (74%). Of the different predictive factors, only FDG PET result significantly correlated with patient outcome (p = 0.0002). PET/CT performance at the end of treatment was as follows: 100% sensitivity, 99% specificity, 89% positive predictive value and 100% negative predictive value. The Kaplan-Meier analysis demonstrated a statistically significant correlation with PFS for FDG PET (p < 0.0001), FLIPI score (0-1 versus >= 2) (p = 0.0451) and number of relapses (none versus >= 1) (p = 0.0058). These findings were confirmed at the univariate analysis, whereas at the multivariate analysis only FDG PET (p = 0.0006892) and number of relapses (p = 0.01947) were independent predictive factors for PFS. Conclusion End-treatment PET/CT in FL has high accuracy and appears to be a good predictor of PFS and patient outcome, irrespective of grading. As expected, patients facing more than one relapse seem to have significantly shorter PFS in the presence of a positive FDG PET.