Case of the Month
Section Editor: Nicholas Stence, MD
Children's Hospital Colorado, Aurora, CO
April 2023
Next Case of the Month Coming May 9...
High-Grade Astrocytoma with Piloid Features (HGAP)
- Background:
- HGAP is a newly described tumor entity that is defined by a unique DNA methylation profile. Previously, tumors with histologic features of pilocytic astrocytomas (PAs) but with increased MIB and other high-grade features were diagnosed as anaplastic pilocytic astrocytomas (APAs), although overall this was not well characterized as a specific tumor type.
- A DNA methylation profile study of histologically defined APAs found a group of tumors with a common profile, called methylation-class anaplastic astrocytoma with piloid features (MC-AA) in the original paper, later termed high-grade astrocytoma with piloid features, although this naming is still being considered. This is one of the first of brain tumors to be defined by a specific DNA methylation profile.
- Outcome analysis has confirmed a worse course than PA but improved over IDH wild-type glioblastoma. Patients are usually older than those diagnosed with PA (median age of 41.5 years, 11% occurred in patients younger than 20 years in the original paper).
- HGAPs are IDH wild-type and often contain deletions of CDKN2A/B, ATRX mutations, and have alterations in the MAPK pathway.
- Subtype analyses have recently designated 3 distinct epigenetic subtypes of HGAP, including 1 associated with NF1 syndrome enrichment, and the original paper also noted 1 or possibly 2 patients with NF1.
- In the original paper, 74% of these tumors were found in the posterior fossa, 17% were supratentorial, and 5% were spinal.
- Key Diagnostic Features:
- Very few imaging descriptions have been published, although tumors have been described as variably T1 hypointense, T2 hyperintense, and heterogeneously enhancing. The tumors did not characteristically restrict diffusion, and no necrosis was reported.
- Treatment:
- In our case, initial therapy consisted of radiation. Most of the tumor responded, although a small nodule developed in the tumor bed following completion of radiation therapy. Dabrafenib/trametinib was added, with resolution of that nodule and stable disease over the course of a year.
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