Background: Lymphoma arising in the central nervous system (CNS) has a dismal prognosis. Although the International Extranodal Lymphoma Study Group (IELSG) scoring system and Memorial Sloan-Kettering Cancer Center (MSKCC) index have been proposed to determining prognosis for patients with PCNSL at diagnosis, there is few study about prognostic factor at mid-treatment. In systemic lymphoma, many clinical studies demonstrated the prognostic significance of interim PET/CT. However, the prognostic role of interim PET/CT in PCNSL is uncertain.

Purpose: This study prospectively investigated that 11C-methionine PET-CT (11C-MET PET) may provide additional prognostic information of mid-response assessment prior to completion of chemotherapy in PCNSL.

Methods: Thirty newly diagnosed patients with PCNSL were enrolled between November 2013 and August 2016. Both brain MRI and 11C-MET PET analysis were performed at the time of diagnosis and after four infusions of high-dose MTX in induction chemotherapy. The clinical prognostic factor was assessed according to International Extranodal Lymphoma Study Group (IESLG) scoring system. Tumor to normal tissue ratio (T/N ratio) and metabolic tumor volume (MTV) were estimated as the indices of interim 11C-MET PET. The optimal cutoff values of T/N ratio and MTV for predicting outcome of PCNSL were identified by receiver operating characteristic (ROC) curve. Survival outcomes were analyzed using the Kaplan-Meier survival curves according to the T/N ratio and MTV of interim PET/CT. The prognostic values of interim T/N ratio and MTV were evaluated by uni- and multivariate cox-regression analysis.

Results: All patients had diffuse large B cell lymphoma with median age of 65.3 years (range: 55-75). Four patients could not be evaluated the interim 11C-MET PET due to disease progression or treatment-related mortality. Four patients proceeded to frontline autologous stem cell transplantation as a consolidation. Patients were categorized into low (N=5, 19.2%), intermediate (N=11, 42.3%) and high (N=10, 38.5%) risk groups according to IELSG prognostic score. Fourteen patients developed a recurrence with median follow-up of 21 months. The discrepancy of interim response between 11C-MET PET and MRI occurred in 4 patients. Whereas no metabolic viable lesions were detected based on interim 11C-MET PET, the remnant contrast enhancing lesions were detected on interim MRI. All four patients achieved complete remission after primary treatment. Progression-free survival (PFS) significantly differed between patients with high and low groups in both of interim T/N ratio (P= 0.003) and MTV (P = 0.023) by the log-rank test. Multivariate cox regression analysis showed a high interim T/N ratio (> 1.67) was significantly associated with a worse progression-free survival (95% CI, 1.03-13.08; P= 0.044).

Conclusion: Interim11C-MET PET based on T/N ratio assessment could be an independent predictive factor in patients with PCNSL.


No relevant conflicts of interest to declare.

Author notes


Asterisk with author names denotes non-ASH members.