CTNI-33. EARLY COMPLETE RESPONSE MIGHT NOT BE AN INDICATOR OF LONGER PROGRESSION-FREE SURVIVAL IN NEWLY-DIAGNOSED PRIMARY CENTRAL NERVOUS SYSTEM LYMPHOMA WITH A COMPLETE RESPONSE BY MTX-BASED INDUCTION THERAPY

Abstract Primary central nervous system lymphoma (PCNSL) is an extra-nodal non-Hodgkin lymphoma solely arising from the central nervous system including eyes. While 70% of patients with newly-diagnosed PCNSL achieve a complete response (CR) after R-MPV, the current standard of care MTX-based induction therapy, recurrence yet frequently occurs (~50%) and clinical factors related to failure are not well defined. Early complete response is associated with lower recurrence rate in various cancers. In this study, we conducted a retrospective, single-institution study to investigate whether early complete response was associated with recurrence in PCNSL. Newly-diagnosed PCNSL patients treated with R-MPV at the authors’ institution between 2011 and 2022 were identified, and progression-free survival (PFS), overall survival (OS) were analyzed along with number of chemotherapy cycles required to achieve a CR or CR unconfirmed (CRu). In total of 92 patients treated with R-MPV identified, 68 (75%) patients achieved a CR or CRu. Among patients who achieved CR or CRu, a median total of seven (1-8) R-MPV cycles were delivered. The median cycle required to achieve CR or CRu was five (1-8). Consolidation whole brain radiation therapy (WBRT) was given to 29 younger patients (median age: 63), while 39 older patients (median age: 74) were treated without WBRT. The number of chemotherapy cycles required to achieve CR or CRu was not associated with PFS or OS in all ages. However, requiring six or more chemotherapy cycles to achieve CR or CRu was associated with longer PFS (p=0.046) in patients treated without WBRT. These data suggest that early complete response might not be indicative of superior survival outcome in newly-diagnosed PCNSL treated without consolidation WBRT. Persisting enhancing lesions during chemotherapy could lead to treatment intensification through delivering greater number of chemotherapy cycles, which might have conferred longer PFS in these patients.