DDEL-11. Subcutaneous rituximab in the treatment of primary CNS lymphoma: a retrospective case series

Abstract Primary central nervous system lymphoma is a rare aggressive lymphoma localized in the CNS, the standard treatment of which consists of induction chemotherapy with a high-dose methotrexate-based regimen because of high CNS bioavailability. The addition of rituximab – a chimeric monoclonal antibody targeting the CD20 antigen on B-cell lymphocytes – to standard chemotherapy has been shown to significantly improve overall survival for patients with systemic diffuse large B-cell lymphoma. Based on encouraging results from several studies, rituximab is now commonly included in standard induction regimens for CD20-positive PCNSL as over 90% of cases are DLBCL. Rituximab is typically administered by intravenous infusion, but this method presents challenges such as the need for trained staff, complex dosing, long infusion times, IV access issues, and risk of infusion-related reactions. Subcutaneous administration may address these issues by being more convenient, potentially improving patient quality of life and treatment adherence. The SC formulation of rituximab also provides trough concentrations comparable to IV administration. In a retrospective review of patient records of the Comprehensive Brain Tumor Service of St Luke’s Medical Center Philippines (2015-2025), four patients who had partial response to induction high-dose methotrexate were subsequently treated with temozolamide and rituximab (initial dose given IV 375mg/m2, then succeeding doses as fixed dose SC 1400mg) every 2 weeks. All achieved complete response after 6 cycles. At 12 months, progression free survival was 100%. Two patients had recurrence outside the CNS but refused further treatment upon recurrence with PFS of 66 and 51 months and OS of 77 and 58 months respectively. The other two patients remain to have no recurrence at the time of writing of this report. No adverse reactions were associated with subcutaneous rituximab and the cost in our institution is comparable to that of the IV preparation. Subcutaneous rituximab appears well-tolerated and potentially more cost-effective in achieving durable complete responses. Larger studies are needed to confirm these results.