Molecular heterogeneity and prognostic biomarkers in primary meningeal melanocytic tumors.

Primary meningeal melanocytic tumors (PMMTs) are rare neoplasms currently stratified by the World Health Organization (WHO) into three grades of malignancy based exclusively on histopathological criteria, while the prognostic significance of molecular alterations remains poorly defined. This study aimed to investigate the prognostic relevance of histopathological and molecular features in PMMTs and to assess the diagnostic utility of immunohistochemical and molecular markers for distinguishing PMMTs from malignant melanotic nerve sheath tumors (MMNSTs). Thirty-six primary central nervous system (CNS) melanocytic tumors, including 24 PMMTs (10 grade 1, 12 grade 2, and 2 grade 3) and 12 MMNSTs, were analyzed through integrated histopathological, immunohistochemical, genetic, and epigenetic characterization. Among grade 2 PMMTs, descriptively defined CNS-invasive otherwise benign melanocytomas defined a clinically favorable subgroup, whereas SF3B1 mutations and chromosome 8q gains were associated with higher recurrence rates and shorter recurrence-free survival. Losses of chromosome 17 or 21q were observed exclusively in MMNSTs, supporting their potential diagnostic utility in distinguishing MMNSTs from PMMTs. These findings demonstrate biological heterogeneity among intermediate-grade PMMTs and identify molecular markers associated with adverse clinical outcomes. Integrated histopathological and molecular characterization may enhance prognostic stratification and diagnostic accuracy in primary CNS melanocytic tumors.