10064- ML-2 CLINICAL CHARACTERISTICS OF NON-COMPLETE RESPONDERS TO MTX-BASED INDUCTION THERAPY IN PATIENTS WITH PRIMARY CNS LYMPHOMA

Abstract BACKGROUND The standard care for primary CNS lymphoma (PCNSL) is high-dose methotrexate (HD-MTX)-based induction therapy including R-MPV followed by consolidation therapy with a high CR/CRu rate. However, non-CR (refractory) patients may face poor prognosis, yet factors predicting response to R-MPV remain unclear. We conducted a retrospective analysis of newly diagnosed PCNSL cases treated with R-MPV at our facility. METHODS A total of 107 patients treated with R-MPV between November 2011 and December 2023 were identified. Clinical background factors, molecular pathological findings, the number of R-MPV cycles, dose reductions or drug discontinuations, response rates, PFS, and OS were analyzed. RESULTS The median age and KPS were 70 years (range 34-90) and 70 (30-90), respectively. Ocular lesions were present in 11 cases (11%), MYD88 mutations were found in 55 (66%), and 26 (38%) were of the GCB subtype. The median number of R-MPV cycles was 7 (1-8), with dose reduction or drug discontinuation in 75 cases (70%). After R-MPV, CR/CRu were achieved in 84 cases (79%), PR in 15 (14%), SD in 2 (2%), and 6 cases had PD (6%), with a non-CR rate of 21.5%. The median PFS was 87.8 months, with median OS not reached and a 5-year OS rate of 79.5%. The median PFS for CR cases was not reached, while for non-CR cases it was 22.5 months (P<0.001). For cases with or without methotrexate or procarbazine dose reduction/discontinuation, PFS was 42.2 months vs. not reached, respectively. The only factor significantly correlated with CR was the number of cycles (P<0.001), with a particularly significant correlation for 4 or more cycles (P<0.001). CONCLUSIONS Fewer number of R-MPV cycles (<4) was significantly associated with non-CR. As non-effective cases might result in early discontinuation, further analysis considering possible confounding factors is necessary.