Abstract: Introduction: Central nervous system (CNS) relapse in diffuse large B-cell lymphoma (DLBCL) is uncommon but is associated with poor outcomes. In selected high risk patients (pts), high dose methotrexate (HDMTX) is often used as CNS prophylaxis with frontline (1L) DLBCL therapy despite uncertain efficacy, optimum dose and timing of delivery. A recent UK study (Wilson et al 2020) showed that intercalated HDMTX (i-HDMTX) was associated with increased toxicity and R-CHOP delays compared to end of treatment (EOT) delivery. Although hypothesis generating, the study size was insufficient to determine whether EOT was non-inferior in terms of CNS relapse risk. Methods: We conducted an international, multicentre retrospective analysis of consecutive DLBCL or high grade BCL pts between 2007-20 from 47 centers in Europe, Australia and N. America. Pts were included if they received R-CHOP or R-CHOP-like 1L therapy with curative intent as well as HDMTX CNS prophylaxis (≥1 cycle). Concurrent intrathecal (IT) prophylaxis was permitted. Pts with known CNS involvement at baseline and those treated with more intensive protocols (e.g. R-DA-EPOCH) were excluded. i-HDMTX was defined as any pt receiving a HD-MTX cycle before the final R-CHOP cycle. CNS relapse events were excluded if occurring after first systemic lymphoma relapse/progression. Time to event endpoints were measured from diagnosis to first event or censor and analysed using Kaplan-Meier and Cox regression methods. Time to CNS relapse was analysed using competing risk Fine and Gray method (for death and non-synchronous systemic relapse). To mitigate for possible immortality bias in the EOT arm, a landmark analysis for pts alive and free from progression at 6 months was conducted. We aimed to exclude a 5% difference in 2-year (y) CNS relapse rates. Results: 1,384 pts were analysed. 750 received i-HDMTX and 634 received EOT HDMTX. Key baseline characteristics are summarised in Table 1. Median follow up was 37.9 months. 44.2% had high CNS IPI (4-6) with no significant difference between i-HDMTX and EOT groups (45.1% vs 43.1%, p=0.087). ≥2 cycles of HDMTX were used in 86.6% with no difference between groups (85.6% vs 87.9%, p=0.22). Concurrent IT prophylaxis use was higher for EOT pts (55.6% vs 38.1% p & lt;0.0001). 78 CNS relapses (42 i-HDMTX, 36 EOT) were observed: parenchymal in 41 (53%), parenchymal and leptomeningeal in 16 (21%) and isolated leptomeningeal in 21 (27%). There was no significant difference in 2y CNS relapse rates between i-HDMTX and EOT in all pts: 5.2% vs 3.9%, adjusted hazard ratio (HR) 0.92 (95% CI 0.58-1.47), p=0.74, 2y difference -0.2% (-2.0-2.5) or landmark analysis: 2.8% vs 4.1%, HR: 0.93 (0.56-1.55), p=0.79, 2y difference: -0.3% (-1.8-2.2%) (Fig 1a/b). Exploratory analyses focusing on pts with isolated CNS relapse (n=57) demonstrated similar results (2y rates 3.6% vs 3.0%, p=0.99). On multivariable analysis (MVA) of risk factors for CNS relapse, renal/adrenal involvement was the only variable associated with increased CNS relapse risk (adjusted HR 1.74 (1.03-2.92), p=0.038). Notably, IT prophylaxis was not associated with reduction in CNS relapse. In 600 high CNS IPI (4-6) pts, there was no difference in CNS relapse risk between i-HD-MTX and EOT (3y rates 9.4% vs 8.6%, HR 0.92 (95% CI 0.52-1.62)). In a composite high risk group including CNS IPI 4-6 and/or any of the following: ≥3 extranodal sites, renal, adrenal, testicular or breast involvement (n=885) there was no difference in 3y CNS relapse rates between groups (i-HDMTX 7.6% vs EOT 7.4%, HR 0.94 (0.58-1.53)). Progression-free survival (PFS) and overall survival (OS) in the i-HDMTX and EOT groups were as follows: 3y PFS 70.7% vs 76.7% (p=0.098), 3y OS 79.9% vs 87.0% (p=0.0016). However, there were no PFS/OS differences between groups on landmark analysis (n=1259) (Fig 1c). On analysis of pts experiencing ≥1 R-CHOP delay of ≥7 days, use of i-HDMTX was the only factor on MVA associated with increased delays (p & lt;0.0001). Discussion: We found no evidence that EOT delivery increases CNS relapse risk when compared to i-HDMTX in this large analysis of pts treated with 1L R-CHOP. Delays to R-CHOP cycles were increased with i-HDMTX. Findings in a high risk subgroup were unchanged and rates of CNS relapse in this HDMTX treated group were similar to published comparable high risk cohorts receiving infrequent CNS prophylaxis. Where HDMTX prophylaxis is used, delivery could be deferred until R-CHOP completion. Figure 1 Figure 1. Disclosures Wilson: Takeda: Other: Conference fees; Janssen: Other: Conference fees; Abbvie: Honoraria. Eyre: Janssen: Honoraria; Secura Bio: Consultancy, Honoraria; Gilead/KITE: Honoraria, Other: Travel support for conferences, Research Funding, Speakers Bureau; Roche: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria, Other: Travel to conferences; AstraZeneca: Honoraria, Research Funding; Loxo Oncology: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy; Beigene: Honoraria, Research Funding. Ahearne: Pfizer: Research Funding; Takeda: Honoraria; Roche: Honoraria. Schorb: Roche: Research Funding; Riemser Pharma GmbH: Honoraria, Research Funding; AbbVie: Research Funding. Ku: Antegene: Consultancy; Roche: Consultancy; Genor Biopharma: Consultancy. Narkhede: Genentech/Roche: Research Funding; Gilead: Research Funding; Genmab: Other: Medical writing support, Research Funding; TG Therapeautics: Research Funding. Lewis: AstraZeneca: Consultancy, Honoraria; Janssen: Honoraria, Patents & Royalties; Novartis: Patents & Royalties; Roche: Consultancy, Honoraria. Øvlisen: Abbvie: Other: Travel expenses. Santarsiere: Janssen: Honoraria. Shah: Abbvie, Janssen and Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees. Roulin: Janssen: Other: Travel and meetings. Manos: Bristol-Myers Squibb: Other: Travel and meetings. Hamad: Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Lopez-Garcia: Roche: Other: Speaker Honoraria, Travel and accommodation grants; Janssen: Other: Speaker Honoraria, Advisor, Travel and accommodation grants, Research Funding; Abbvie: Other: Speaker Honoraria, Advisor, Travel and accommodation grants; Celgene: Other: Speaker Honoraria; Fresenius: Other: Speaker Honoraria; Novonordisk: Other: Speaker Honoraria. El-Galaly: ROCHE Ltd: Ended employment in the past 24 months; Abbvie: Other: Speakers fee. Cheah: Beigene: Consultancy, Honoraria, Other: advisory; AbbVie: Research Funding; Celgene: Research Funding; AstraZeneca: Consultancy, Honoraria, Other: advisory; Loxo/Lilly: Consultancy, Honoraria, Other: advisory; TG Therapeutics: Consultancy, Honoraria, Other: advisory; Roche: Consultancy, Honoraria, Other: advisory and travel expenses, Research Funding; Janssen: Consultancy, Honoraria, Other: advisory; MSD: Consultancy, Honoraria, Other: advisory, Research Funding; Gilead: Consultancy, Honoraria, Other: advisory; Ascentage pharma: Consultancy, Honoraria, Other: advisory. Ferreri: Gilead, Novartis, Juno, PletixaPharm, Roche, Incyte: Membership on an entity's Board of Directors or advisory committees; BMS, Beigene, Pharmacyclics, Hutchison Medipharma, Amgen, Genmab, ADC Therapeutics, Gilead, Novartis, Pfizer: Research Funding. Fox: Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Other: speaker fees. Cwynarski: Gilead: Consultancy, Speakers Bureau; Incyte: Consultancy, Speakers Bureau; Atara: Consultancy; Celgene: Consultancy; Takeda: Consultancy, Other: travel to scientific conferences, Speakers Bureau; Kite, a Gilead Company: Consultancy, Other: travel to scientific conferences, Speakers Bureau; Janssen: Consultancy, Other: travel to scientific conferences; Roche: Consultancy, Other: travel to scientific conferences, Speakers Bureau; BMS/Celgene: Other: travel to scientific conferences. McKay: Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Other: Travel Support; KITE: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel Support; Janssen: Honoraria, Other: Travel Support; Beigene: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS/Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Abstract: Prophylactic high-dose methotrexate (HD-MTX) is often used for diffuse large B-cell lymphoma (DLBCL) patients at high risk of central nervous system (CNS) relapse, despite limited evidence demonstrating efficacy or the optimal delivery method. We conducted a retrospective, international analysis of 1384 patients receiving HD-MTX CNS prophylaxis either intercalated (i-HD-MTX) (n = 749) or at the end (n = 635) of R-CHOP/R-CHOP-like therapy (EOT). There were 78 CNS relapses (3-year rate 5.7%), with no difference between i-HD-MTX and EOT: 5.7% vs 5.8%, P = .98; 3-year difference: 0.04% (−2.0% to 3.1%). Conclusions were unchanged on adjusting for baseline prognostic factors or on 6-month landmark analysis (n = 1253). In patients with a high CNS international prognostic index (n = 600), the 3-year CNS relapse rate was 9.1%, with no difference between i-HD-MTX and EOT. On multivariable analysis, increasing age and renal/adrenal involvement were the only independent risk factors for CNS relapse. Concurrent intrathecal prophylaxis was not associated with a reduction in CNS relapse. R-CHOP delays of ≥7 days were significantly increased with i-HD-MTX vs EOT, with 308 of 1573 (19.6%) i-HD-MTX treatments resulting in a delay to subsequent R-CHOP (median 8 days). Increased risk of delay occurred in older patients when delivery was later than day 10 in the R-CHOP cycle. In summary, we found no evidence that EOT delivery increases CNS relapse risk vs i-HD-MTX. Findings in high-risk subgroups were unchanged. Rates of CNS relapse in this HD-MTX-treated cohort were similar to comparable cohorts receiving infrequent CNS prophylaxis. If HD-MTX is still considered for certain high-risk patients, delivery could be deferred until R-CHOP completion.