Loss of meningothelial identity and mesenchymal fate switching in NF2-mutant meningiomas.

Intracranial sarcomas can arise secondarily from primary brain tumors, including gliomas and meningiomas, either spontaneously or following radiotherapy. The current WHO classification recognizes sarcomatous transformation in several tumor entities; however, sarcomas arising from meningiomas remain poorly characterized and are regarded as a possible histological manifestation within the spectrum of anaplastic meningiomas. We analyzed nine matched meningioma-sarcoma pairs using integrated histopathological assessment and molecular profiling, including DNA methylation analysis, next-generation sequencing, copy number profiling, and proteomics. Although recurrent sarcomatous tumors were clonally related to their meningioma precursors-sharing identical NF2 alterations and overlapping chromosomal aberrations-they demonstrated pronounced divergence at the histological, immunophenotypic, and epigenetic levels. Importantly, sarcomatous transformation occurred in four cases without prior radiotherapy. Sarcomatous recurrences exhibited loss of meningothelial markers and acquired expression of cytokeratin and myogenic markers. DNA methylation profiling revealed a shift away from canonical meningioma signatures toward profiles resembling non-meningothelial mesenchymal tumors. Proteomic analysis showed consistent upregulation of SOX2 in sarcomatous tumors compared with their primary counterparts, suggesting acquisition of stem-like features during lineage divergence. Clinically, these tumors were associated with aggressive growth, early recurrence, and extracranial metastases, resembling malignant sarcomas more closely than anaplastic meningiomas. In addition, analysis of an institutional cohort of NF2-mutant intracranial tumors (n = 316) suggests that sarcomas with inactivating NF2 mutations may originate from meningiomas even in the absence of a clinically recognized precursor. Together, these findings suggest that sarcomatous transformation represents a rare evolutionary endpoint in NF2-mutant meningiomas, marked by clonal continuity but pronounced biological divergence. These results highlight limitations of morphology-based classification and emphasize the value of integrated molecular diagnostics in distinguishing these tumors from conventional high-grade meningiomas. Given their sarcoma-like behavior despite a meningioma ancestry, these tumors may not be adequately captured by current meningioma grading schemes.