Ncog-40. patterns of progression in patients with newly diagnosed primary central nervous system lymphoma following treatment with high-dose methotrexate

Abstract INTRODUCTION Primary central nervous system lymphoma (PCNSL) is a rare form of non-Hodgkin's lymphoma that primarily affects the brain. Recurrence of PCNSL within the central nervous system is common, but patterns of intracranial recurrence following induction chemotherapy have not been extensively studied. This study aims to elucidate the patterns of recurrence and progression in PCNSL. METHODS Adult patients from two institutions with newly diagnosed PCNSL that received HD-MTX based chemotherapy from 2011-2023 were included. Patient charts and diagnostic imaging were retrospectively reviewed. The pattern of recurrence/progression was reviewed by comparing the initial diagnostic MRI to the first recurrence MRI (T1 post-contrast and FLAIR sequence). Distant recurrences were defined as separate lesions from the previous primary enhancing lesion, located outside the initial FLAIR abnormality observed on imaging. Local recurrences were characterized as new lesions overlapping with the primary enhancing lesion/FLAIR abnormality. RESULTS 25 patients were identified to have been diagnosed with PCNSL and progressed through initial definitive treatment with HD-MTX based chemotherapy. 2/25 received initial management with radiation therapy. Median age at diagnosis was 66 years. The median time to progression was 18.1 months (Range; 0.9-70). Twelve of the 25 patients had a complete response to initial systemic therapy, 6 had a partial response, and 7 patients had disease progression through chemotherapy. Eleven of the 25 patients were found to have multifocal disease at diagnosis. 13/25 (52%) patients had distant recurrence only, 5/25(20%) had only local recurrence, and 7/25 (28%) displayed both local and distant recurrence pattern. CONCLUSION In this retrospective review, for patients diagnosed with PCNSL who are able to undergo HD-MTX we identified that the majority of disease recurrence is outside or distant to the primary disease site vs locally (80% vs 20%). Such findings should be verified with a larger cohort and can help direct further consolidation strategies.