Spinal high-grade astrocytoma with piloid features arising in a patient with molecularly confirmed cerebellar pilocytic astrocytoma.

Pilocytic astrocytoma (PA) is a benign tumor with a low risk of high-grade transformation. High-grade astrocytoma with piloid features (HGAP) is a recently recognized tumor entity that may arise de novo or from low-grade gliomas. Here, we report a patient harboring both a fourth ventricular PA and a spinal cord tumor. Methylation profiling classified the brain tumor as PA and the spinal tumor as HGAP. Both tumors shared a KIAA1549::BRAF fusion with identical DNA breakpoints, confirming a common clonal origin. The spinal tumor also showed complex chromosome copy number aberrations, including homozygous deletion of CDKN2A/B. These findings suggest additional molecular alterations associated with tumor progression within the piloid lineage. To our knowledge, this is the first report providing comprehensive, paired molecular characterization of both PA and HGAP in the same patient, offering insight into their potential evolutionary relationship.