Purpose: The purpose of our study was to assess the predictive and prognostic role of 2-18F-fluoro-2-deoxy-D-glucose (FDG) PET/MRI during high-dose methotrexate-based chemotherapy (HD-MBC) in de novo primary central nervous system lymphoma (PCNSL) patients aged 60 and above.
Methods: This prospective multicentric ancillary study included 65 immunocompetents patients who received induction HD-MBC as part of the BLOCAGE01 phase III trial. FDG-PET/MRI were acquired at baseline, post two cycles (PET/MRI2), and post-treatment (PET/MRI3). FDG-PET response was dichotomized, with "positive" indicating persistent tumor uptake higher than the contralateral mirroring brain region. Performances of FDG-PET and International PCNSL Collaborative Group criteria in predicting induction response, progression-free survival (PFS), and overall survival (OS) were compared.
Results: Of 48 PET2 scans performed, nine were positive and aligned with a partial response (PR) on MRI2. Among these, eight (89%) progressed by the end of the induction phase. In contrast, 35/39 (90%) of PET2-negative patients achieved complete response (CR). Among the 18 discordant responses at interim (PETCR/MRIPR), 83% ultimately achieved CR. 87% of the PET2-negative patients were disease-free at 6 months versus 11% of the PET2-positive patients (p<0.001). The MRI2 response did not significantly differentiate patients based on their PFS, regardless of whether they were in CR or PR. Both PET2 and MRI2 independently predicted OS in multivariate analysis, with PET2 showing stronger association.
Conclusion: Our study highlights the potential of interim FDG-PET for early management of PCNSL patients. Response-driven treatment based on PET2 may guide future clinical trials.
Keywords: Early assessment; FDG; PET/MRI; Primary central nervous system lymphoma; prognosis.
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