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Produced: 09/04/2025 11:57 PM
Question 20240009
Inquiry Details
References:
#1: WHO Class CNS Tumors, 4th ed.: pp.10, 16-89; 5th ed.: pp.8-93. 4th and 5th editions
#2: Solid Tumor Rules. Malignant CNS and Peripheral Nerves, March 2023 Update
Question:
Solid Tumor Rules/Histology --Brain and CNS: Why is high grade astrocytoma with piloid features (HGAP) not grouped together with the other astrocytoma histologies as a subtype/variant of astrocytoma? See Discussion.
Discussion:
It appears there was some confusion about finding this new malignant HGAP tumor (2023+) code. If this is not a specific subtype/variant of astrocytoma, can clarification be added to the “New for 2023” entry for HGAP?
Answer:
HGAP is listed as a separate classification and is not a subtype of the diffuse gliomas. WHO Classification of Tumors of the Central Nervous System, 5th edition, has two categories dealing with non-pediatric astrocytic tumors:
Adult-type diffuse gliomas
Circumscribed astrocytic tumors
HGAP falls into the second category as a result of updates to the 4th edition WHO classification in 2016 with advances in the role of molecular diagnostics with the 5th edition. All astrocytic tumors were previously grouped together whereas not all diffuse gliomas (astrocytic or not) are grouped together on the basis of growth pattern and behaviors, and shared IDH1 and IDH2 genetic status. The new classification separates astrocytomas that have a more circumscribed growth pattern, lack IDH gene alterations, and sometimes have BRAF mutations (i.e., pilocytic astrocytoma). The impact of molecular advances has driven classification changes as described in the 5th edition.
Review of site/histologiy combinations for CNS neoplasms is currently being performed by Cancer PathCHART experts. It's possible they will recommend HGAP be moved to a subtype/variant of astrocytoma, NOS.
