Outcome of Patients With Central Nervous System Multiple Myeloma (CNS-MM) Treated With CNS-Directed Radiation Therapy

Background: The prognosis of multiple myeloma involving the central nervous system (CNS-MM) is poor. We report outcomes of CNS-MM treated with CNS-directed radiation therapy (RT). Methods: We retrospectively reviewed patients with CNS-MM treated with CNS-directed RT from 2015 to 2024. CNS-MM was defined as having radiographic leptomeningeal or parenchymal disease, and/or pathologic CSF involvement. Complete response (CR) constituted having no atypical cells in CSF or resolution of radiographic disease. Otherwise, patients were categorized with partial response (PR) based on imaging, or stable disease (SD). The Kaplan-Meier method was used to estimate survival. Results: Of 45 patients with CNS-MM, 28 (62.2%) had high-risk disease. Median overall survival (OS) was 3.7 months (range: 0.4-52.2) postdiagnosis of CNS-MM. Most patients (n = 22, 48.9%) underwent craniospinal irradiation; 9 received whole brain RT (20%), and the others received focal brain or spine RT. The median dose was 20 Gy (2-30 Gy) in 10 fractions (1-15). Due to death or discharge to hospice before further follow-up of treatment efficacy (n = 24), only 21 patients (46.7%) were evaluable post-RT with adequate CSF or radiographic follow-up. For these evaluable patients, post-RT CR occurred in 14 patients (66.7%), PR in 5 (23.8%), and SD in 2 (9.5%). For patients with CR after RT, the median OS was 7.3 months (3-52.2) from CNS-MM diagnosis. Focal brain CNS-MM associated with improved OS and likelihood of attaining long-term survival with CNS CR. Conclusion: Aggressive multimodality therapy including RT may induce durable CNS control in a small subset of patients with CNS-MM, a high-risk population.