CUX1::MET fusion defines an indolent subtype of diffuse low-grade glioma, MAPK pathway-altered.

Diffuse low-grade glioma, MAPK pathway-altered (DLGG-MAPK), is a recently defined tumor entity characterized by genetic alterations activating the MAPK signaling cascade. While BRAF and FGFR alterations are most frequently reported, the biological and clinical significance of other MAPK-activating events remains poorly understood. We report a 25-year-old woman with a right temporal lobe tumor harboring a novel CUX1::MET fusion. The lesion was initially detected at age 10 during neuroimaging performed for a transient headache and subsequently followed an indolent clinical course for approximately 15 years before manifesting with acute hemorrhage. Histologically, the tumor showed diffuse infiltration with oligodendroglioma-like morphology, absence of high-grade features, and a low proliferative index. Molecular analysis identified an in-frame CUX1::MET fusion retaining the MET kinase domain, resulting in exon 14 skipping and activation of the MAPK pathway. Despite the presence of a MET alteration typically associated with aggressive tumors, the lesion demonstrated prolonged indolence and low-grade biological behavior. To our knowledge, this is the first case report demonstrating the presence of a CUX1::MET fusion in DLLG-MAPK. This case expands the molecular spectrum of DLGG-MAPK and provides novel insight into the biological heterogeneity of MET-driven gliomas, suggesting that MET fusion alone is insufficient to confer high-grade behavior in this tumor context.