The prognostic value of mid- and post-treatment [¹⁸F]fluorodeoxyglucose (FDG) positron emission tomography (PET) in indolent follicular lymphoma

[¹⁸F]fluorodeoxyglucose positron emission tomography (PET) is a useful staging investigation for follicular lymphoma (FL). Recent studies have shown that positive post-treatment PET is also a strong predictor of inferior overall survival. To evaluate the predictive value of mid- and post-treatment PET in FL patients with respect to progression-free survival (PFS) and overall survival (OS). We included 57 patients with indolent FL (grade 1, 2, and 3a) who received induction chemotherapy. Mid- and post-treatment PET results were correlated with Mid- and post-treatment PET results were correlated with PFS and OS retrospectively and analysed using Kaplan-Meier survival analysis and Cox regression. Post-treatment PET was predictive of OS (mean OS 95.2 vs. 45.0 months for PET-negative vs. PET-positive, p < 0.001) and showed a trend towards significance for PFS (mean PFS 74.4 vs. 38.2 months for PET- vs. PET, p=0.083). 3-year PFS for post-treatment PET- and PET patients were 72 and 30%, respectively. 3-year OS were 96 and 60%, respectively. Mid-treatment PET was not predictive of PFS (mean PFS 78.5 vs. 51.0 months for PET- vs. PET, p=0.35) nor OS (mean OS 89.9 vs. 76.6 months for PET- vs. PET, p=0.92). Post-treatment PET is predictive of OS in indolent FL. It identifies patients who might benefit from more intensive follow-up, enrolment in clinical trials or second-line therapy. Mid-treatment PET scan results did not appear to predict long-term treatment outcomes. (author)