BRAF and pilocytic astrocytoma: Of the most frequent non-diffuse gliomas, pilocytic astrocytomas are almost always affected by single abnormalities of the mitogen-activating protein kinase (MAPK) pathway (most frequently by KIAA1549-BRAF fusion, in other cases by a BRAF V600E or other mutation affecting this pathway), indicating that this neoplasm may be a ‘one pathway’ disease [33].