Circumscribed Meningeal Melanocytic Neoplasms: CNS WHO Grade, Molecular Profile, and Clinical Outcomes

Circumscribed meningeal melanocytic neoplasms (CMMNs) represent a spectrum of rare central nervous system (CNS) tumors. Knowledge of their clinical behavior and molecular correlates remains limited. In this single-institution retrospective study, we analyzed 31 patients (14 male, 17 female; median age, 59 years) diagnosed with CMMN between 2004 and 2025. In this patient cohort, based on the current World Health Organization Central Nervous System Tumor Classification (WHO CNS5) criteria, the majority of cases (18, 58.1%) fell into the intermediate-grade melanocytic tumor (IMT) category based on histology, with either increased mitotic activity, CNS invasion, or both; 7 (22.6%) were melanocytomas, 5 (16.1%) melanomas, and 1 (3.2%) indeterminate case because of limited tissue. By next-generation sequencing, mutations were identified in GNAQ/GNA11 in 21/24 cases, BAP1 in 5/23 (2 IMT, 3 melanoma), EIF1AX in 9/21 (1 melanocytoma, 8 IMT), and SF3B1 in 3/23 (2 IMT, 1 melanoma). Primary sites were spinal (20), posterior fossa (6), and supratentorial (5). During follow-up, progression was observed in 5/6 melanocytomas, 9/13 IMTs, and 4/5 melanomas, suggesting a high frequency of progression across all groups. Two-year progression-free survival was 83.3% (95% confidence interval [CI], 53.5%-100.0%) for melanocytoma, 55.9% (95% CI, 26.7%-85.2%) for IMT, and 25.0% (95% CI, 0.0%-67.4%) for melanoma. Five-year overall survival (OS) was 80.0% (95% CI, 44.9%-100.0%) for melanocytoma, 65.3% (95% CI, 37.0%-93.6%) for IMT, and 0.0% for melanoma. OS was significantly worse in melanoma compared with melanocytoma (p = 0.002). BAP1 mutation correlated with worse OS (hazard ratio 8.73, p = 0.006). Upfront maximal safe resection appeared to be associated with improved outcomes in selected patients, whereas radiotherapy and systemic therapy did not demonstrate clear additional benefit in this cohort. In summary, our study shows that all CMMNs, irrespective of grade, have a high propensity to recur and melanoma histology and BAP1 mutation are associated with significantly worse OS.