Outcomes of stereotactic radiosurgery in central nervous system lymphoma: A single institution experience

e14061 Background: Primary or systemic high-grade B-cell lymphoma with secondary central nervous system lymphoma (PCNSL or SCNSL) are currently treated with high-dose methotrexate (HD-MTx) based chemo-immunotherapy regimens with/without whole brain radiation therapy (WBRT). CNS relapse can occur in up to 50% of patients with PCNSL or SCNSL. WBRT has been used as a salvage therapy for those patients. However, long-term neurological toxicities significantly reduce its clinical benefit. Stereotactic radiosurgery (SRS) is the administration of a localized, high dose of ionizing radiation. Limited studies exist exploring SRS as a treatment modality in relapsed/refractory (r/r) PCNSL/SCNSL. Methods: We conducted a retrospective single-center study evaluating the clinical efficacy of SRS in r/r PCNSL/SCNSL. Demographic, clinical, pathological, and treatment characteristics were collected in 29 r/r PCNSL (N=17)/SCNSL (N=12) patients, age ≥ 18 years, who received SRS between 01/2000 and 01/2023. Progression-free survival (PFS) and overall survival (OS) were calculated and reported using Kaplan-Meier analyses and log-rank tests. Results: Baseline characteristics are summarized (Table). The median Karnofsky performance status and Charlson comorbidity index were 70 and 5 respectively. For patients with PCNSL (N=17), the most common prior chemotherapy regimen administered was rituximab (R) in combination with the DeAngelis regimen (N=12), followed by the MATRIX regimen (N=3). In patients with SCNSL, the most common systemic chemotherapy regimen used was R + CHOP (N=9). Few patients received temozolomide (N=2). 5/29 (17%) of patients received WBRT before SRS. The overall response rate (ORR) to SRS in r/r PCNSL was 60% (7 CR and 2 PR). The ORR in r/r SCNSL was 83% (7 CR and 3 PR). The median OS of the overall cohort was 7.0 months (95% CI 5.1-8.9), while the median PFS was 5.0 months (95% CI 1.2-8.7). For patients with PCNSL, the median OS was 10.0 months (95% CI 2.2-17.7), and only 7 months (95% CI 1.8-12.1) for patients with SCNSL. Prior WBRT was associated with worse survival outcomes. Of interest, WBRT was avoided in 24/24 patients (100%). Conclusions: Our data support that CNSL patients can benefit from SRS therapy, with acceptable OS and PFS. In addition, the disease control spared patients from WBRT and therefore, mitigated neurological complications associated with that modality. [Table: see text]