Tip-140; High Grade Astrocytoma with Piloid Features

Tip-140; Pilocytic astrocytoma is the prototype of circumscribed gliomas, that occurs commonly in the posterior fossa, in the form of a mural nodule in a cystic lesion. It is associated with MAPK pathway gene alterations, most often KIAA1549::BRAF gene fusions. It is a CNS WHO grade 1, that is cured mostly with gross total resection. High-grade astrocytoma with piloid features, HGAP, is an astrocytoma often with high-grade piloid and/or glioblastoma-like histological features. In about a third of cases, eosinophilic granular bodies or Rosenthal fibers are observed. This is associated with alterations of MAPK pathway genes like pilocytic astrocytoma, often combined with homozygous deletion involving the CDKN2A and/or CDKN2B locus, and/or ATRX mutation or loss of nuclear ATRX expression. HGAP shows a distinct DNA methylation profile. Most frequently, HGAP originates in the posterior fossa, typically affecting the cerebellum in 74% of cases. It typically occurs in adults with a median age of 40 years. Although it mostly arises de novo, some cases develop from a pre-existing lower-grade astrocytic tumor, including pilocytic astrocytoma, like in this case.