Distal noncontiguous recurrence and sarcomatous transformation of glioblastoma with stable molecular profile: illustrative case.

Glioblastoma (GB) typically recurs locally and maintains a glial histopathological phenotype. Sarcomatoid transformation is rare, and distal extra-axial recurrence with bone and soft tissue involvement is exceptionally uncommon. Molecular features of such sarcomatoid transformations remain poorly described. The authors present the case of a 53-year-old man with a history of right temporal GB (IDH-wildtype, MGMT-unmethylated) treated with maximal safe resection and chemoradiotherapy. Eleven months postoperatively, surveillance MRI demonstrated local enhancement with a new left parasagittal extra-axial lesion with bony and subgaleal extension. Debulking and resection revealed a high-grade sarcomatoid tumor with focal glial immunophenotype, mimicking a secondary gliosarcoma but with near-complete predominance of the sarcomatous component. Molecular analysis demonstrated preservation of TERT, PIK3CA, and PTEN variants identified in the original GB, with acquisition of a TP53 mutation. This case illustrates a rare pattern of GB progression, characterized by distal extra-axial recurrence with sarcomatoid transformation. The shared driver TERT, PIK3CA, and PTEN mutations in the original right temporal and subsequent left extra-axial lesion support clonal evolution, while the newly acquired TP53 alteration may underlie histological shift. Clinicians should consider histological transformation when evaluating atypical or extracranial recurrences, as molecular continuity with the primary tumor can guide interpretation of tumor biology and recurrence patterns. https://thejns.org/doi/10.3171/CASE25714.