Impact of meningeal dissemination (MD) on outcome in primary CNS lymphoma in the G-PCNSL-SG1 trial

2026 Background: The prognostic impact of MD in PCNSL is still debated. Within the framework of a multicenter randomized trial (G-PCNSL-SG1) we evaluated patients for outcome according to the presence of MD. Methods: Immunocompetent adult patients were initially treated with up to six cycles of high-dose methotrexate (HD-MTX; 4g/m2) based chemotherapy without intrathecal therapy. Those randomized to radiotherapy subsequently received whole-brain radiotherapy (WBRT) with 45 Gy, in 1.5 Gy fractions; those randomized to chemotherapy did not receive further therapy in case of complete remission or high-dose cytarabine when complete response was not achieved. MD was defined by the presence of lymphoma cells in the CSF detected by at least one of the following methods: cytomorphology, detection of clonal B cells by IgH-PCR or contrast enhancement of the leptomeninges on MRI. Results: All 526 patients fulfilling the eligibility criteria were entered into the analysis. MD at presentation was detected in 104 (19.8...