FGFR1 and pilocytic astrocytoma: FGFR1 partial duplication involving the tyrosine kinase domain (FGFR1 TKD) has been identified in pilocytic astrocytoma (WHO grade 1 tumor), diffuse astrocytoma (grade 2), dysembryoplastic neuroepithelial tumor (DNT) (grade 1), and diffuse low-grade glioma, MAPK pathway-altered (2).