BACKGROUND: Intravascular large B-cell lymphoma (IVLBCL) is a rare type of extranodal large B-cell lymphoma for which prognosis is typically poor without a timely diagnosis. To explore the safety and efficacy of standard chemotherapy combined with central nervous system (CNS)-directed therapy, we conducted a multicentre, single-arm, phase 2 trial in untreated IVLBCL patients without CNS involvement at diagnosis (PRIMEUR-IVL). In the primary analysis, the PRIMEUR-IVL study demonstrated 2-year progression-free survival (PFS) of 76% and 2-year overall survival (OS) of 92% with a low incidence (3%) of secondary CNS involvement (sCNSi). METHODS: We present a prespecified final analysis of the PRIMEUR-IVL study including 5-year PFS, OS and cumulative incidence of sCNSi. Participants were enrolled between June 2011 and July 2016, and the data cutoff date for the final analysis was 16 November 2021. The trial was registered in the UMIN Clinical Trial Registry (UMIN000005707) and the Japan Registry of Clinical Trials (jRCTs041180165). FINDINGS: With a median follow-up of 7.1 years (interquartile range 5.6-8.7), 5-year PFS in all 37 eligible patients was 68% (95% confidence interval [CI] 50%-80%) and OS was 78% (95% CI 61%-89%). No additional sCNSi was observed after the primary analysis. Severe adverse events after the primary analysis were grade 4 neutropenia (n = 1) and grade 4 myelodysplastic syndrome that did not require specific treatment (n = 1). Eight deaths occurred during the observation period after enrolment, due to primary disease (n = 6), sepsis (n = 1) and unknown sudden death (n = 1). INTERPRETATION: Long-term follow-up data demonstrated durable response for PFS and OS, and low cumulative incidence of sCNSi, indicating the efficacy of standard chemotherapy combined with CNS-directed therapy for untreated IVLBCL patients. FUNDING: This study received financial support from the Japan Agency for Medical Research and Development, Center for Supporting Hematology-Oncology Studies, and National Cancer Center.