CDKN2A/B Loss Is Associated with Anaplastic Transformation in a Case of NTRK2 Fusion‐positive Pilocytic Astrocytoma

Pilocytic astrocytomas are typically grade I astrocytomas, only rarely progressing to anaplastic counterparts [ 1 ]. In the case of anaplastic pilocytic astrocytomas, some are associated with neurofibromatosis type 1 (NF1) [ 2 ], others are associated with radiation treatment [ 2 ], and the remainder appear de novo. These de novo tumours can be particularly challenging to distinguish from glioblastomas, which are grade IV and carry a worse prognosis. Here we report an unusual case of malignant transformation of a pilocytic astrocytoma in the absence of NF1 alterations or radiation treatment.