18F-FDG PET Is an Independent Outcome Predictor in Primary Central Nervous System Lymphoma

Primary central nervous system (CNS) lymphoma is an aggressive non-Hodgkin lymphoma with poor prognosis. We evaluated pretreatment 18F-FDG PET as a prognostic marker in primary CNS lymphoma. Methods: Forty-two immunocompetent patients with newly diagnosed primary CNS lymphoma who underwent pretreatment 18F-FDG PET were retrospectively analyzed. Baseline status and response to treatment were evaluated by MR imaging. Tumor maximum standardized uptake values were assessed by volume-of-interest analyses using an automatic isocontour definition. A 10-step semiquantitative visual rating system (metabolic imaging lymphoma aggressiveness scale, or MILAS) was used to assess primary CNS lymphoma metabolism as a marker of clinical aggressiveness. Logistic regression, log-rank testing, and multivariable Cox regression were used to investigate the association between 18F-FDG uptake and tumor response and survival. Results: Mean maximum standardized uptake value correlated linearly with MILAS. The distribution of patients according to MILAS (0–9) was 0%, 28.6%, 23.8%, 21.4%, 11.9%, 4.8%, 7.1%, 0%, 0%, and 2.4%. There was no correlation between MILAS and response to treatment. Respective 2- and 5-y survival rates were 52% and 32% for progression-free survival (PFS) and 64% and 50% for overall survival (OS). A cutoff at MILAS 3 was a good separator for PFS (median: 54.7 mo [≤3], 3.8 mo [>3], P = 0.0272) and OS (median: not reached [≤3], 13.8 mo [>3], P = 0.131). In multivariable analyses, increasing MILAS was significantly associated with shorter PFS (hazard ratio, 1.49, P = 0.006) and OS (hazard ratio, 1.43, P = 0.018). Conclusion: Increased pretreatment 18F-FDG uptake may offer new opportunities for baseline risk evaluation in untreated primary CNS lymphoma.