Stereotactic Radiation Therapy With Concurrent Immune Checkpoint Inhibitor Therapy in Patients With Relapsed or Refractory Central Nervous System Lymphoma

Abstract

Relapsed or refractory central nervous system lymphoma (CNSL) after high-dose methotrexate-based therapy is a challenging clinical entity with limited treatment options. Salvage systemic therapy and whole brain radiation therapy (WBRT) are commonly employed but are associated with significant toxicity and poor outcomes. Prior studies have shown that primary CNSLs frequently exhibit increased expression of PD-L1, and immune checkpoint inhibitor (ICI) therapy may be active in this setting. We assessed the safety and efficacy of concurrent ICI therapy and hypo-fractionated stereotactic radiation therapy (SRT) in patients with relapsed or refractory CNSL.We retrospectively analyzed the records of patients with relapsed or refractory CNSL treated with SRT + ICI at our institution from 2017 to 2020. ICI therapy included pembrolizumab 200 mg IV q3weeks or nivolumab 3 mg/mg IV q2weeks. Linac-based SRT was delivered in 5 daily fractions of 5 Gy. CTVs included all grossly enhancing disease on T1 weighted post-contrast MR scans, with 3 mm uniform PTV expansions. Patients were followed for symptomatic and radiographic response. Progression-free survival (PFS) and overall survival (OS) were calculated via Kaplan-Meier analysis.Seven consecutive patients with relapsed or recurrent CNSL were analyzed: 6 with primary CNSL, 1 with secondary CNSL. Patients presented at a median age of 72.2 years (range: 40.9 - 89.9) after a median of 2 prior courses of systemic therapy. Five patients had a solitary intracranial lesion and 2 had multiple lesions. None had active extracranial disease. Median pre-SRT Karnofsky Performance Status (KPS) was 60 (range 50 - 90). All 7 patients completed SRT and received concurrent and adjuvant ICI therapy. Median follow-up after completion of SRT was 9.1 months. Acute toxicities of SRT and ICI therapy were minimal, including fatigue (3 patients), diarrhea (2), and adrenal insufficiency requiring oral steroids (1). Five patients (71.4%) achieved symptomatic improvement after SRT including 2 patients (28.5%) with a clinical complete response (CR). Median post-SRT KPS was 70 (range: 60 - 100). Six patients had follow-up imaging, and all had an objective response including 3 (50%) with a radiographic CR. The median time to best radiographic response was 2.0 months (range 0.3 - 3.7 months), and all treated lesions remained controlled on all subsequent imaging. Three patients (42.9%) experienced out-of-field intracranial recurrence. Median PFS was 7.7 months (95% CI: 4.0 - 11.4 months) and median OS was 12.6 months (95% CI: 7.5 - 12.7 months) post-SRT.Among patients with relapsed or refractory CNSL, SRT + ICI appears to be well tolerated and offers excellent symptomatic and radiographic local control. Further studies are needed to identify appropriate candidates for salvage SRT + ICI, and to evaluate the clinical efficacy and neurocognitive impact of this approach.