CTNI-40. HIGH-DOSE METHOTREXATE, RITUXIMAB, AND TEMOZOLOMIDE (MR-T) FOR INDUCTION THERAPY FOR PRIMARY CENTRAL NERVOUS SYSTEM LYMPHOMA – A SINGLE CENTER RETROSPECTIVE ANALYSIS

Abstract High-dose methotrexate-based (HD-MTX) regimens are the backbone of primary central nervous system lymphoma (PCNSL) induction treatment, often combined with rituximab and alkylators. MT-R is a commonly utilized regimen that was established in the Alliance 50202 study, consisting of HD-MTX 8gm/m2 given every 14 days, rituximab 375mg/m2 given for six weekly doses, and temozolomide 150mg/m2 given for 5 days every 28 days for four months. Here, we report results of an alternative and less intensive regimen (MR-T) using the same agents. We performed a single-center retrospective analysis of newly diagnosed PCNSL patients (Jan 2017 to May 2025) treated with HD-MTX 3.5 g/m2 given every 21 days for up to 8 doses, rituximab 500mg/m2 given every 21 days for 6 doses, and temozolomide 150mg/m2 given for 5 days every 28 days for up to 4 months. Thirty-nine patients were treated (17 men, 22 women). Median age at diagnosis was 65 (range 28 - 89). Median KPS was 80 (range 60-90), 31 patients (79%) received at least 6 cycles of HD-MTX, 3 patients (7%) had acute kidney injury requiring HD-MTX discontinuation. Median hospital length of stay was 4 days, 72% of patients achieved a CR/CRu at the end of induction treatment, 71% of patients < 70 years of age proceeded to HDC-ASCT consolidation. With 28.7 months of median follow-up time, the median PFS and OS for all patients was 28.6 and 32.7 months, respectively, 2-year PFS and OS was 77% and 85%, respectively, for patients who underwent HDC-ASCT, 2-year PFS and OS was 75% for patients age > 70 years. This less intensive regimen of MR-T demonstrated favorable complete response rates, survival, and toxicity profile for newly diagnosed PCNSL patients, including elderly patients, comparable to other well-established regimens.