Tuesday, September 20, 2016

CAP16 Abstract Highlights - Astrocytoma With a Distinct Molecular Signature: MYB Rearrangement and EGFR Amplification

The 2016 annual meeting of the College of American Pathlologists (CAP16) is coming up September 25-28 in Las Vegas. In this series of posts, I'll be featuring poster abstracts of particular interest to neuropathologists.

Doan V. Lai and colleagues at Oklahoma University and St. Jude's in Memphis in Poster #184 describe a combination of low- and high-grade molecular features in a pediatric diffuse astrocytoma.

Diffuse gliomas are uncommon in children but cause significant morbidity and mortality. Unlike diffuse gliomas in adults, pediatric low-grade tumors rarely progress to high-grade disease. Molecular studies are playing an increasingly large role in classifying and predicting therapeutic response in these tumors. MYB rearrangements are common in pediatric diffuse low-grade astrocytomas. EGFR amplification, which occurs in high-grade gliomas, however, is not reported in low-grade gliomas. We report the first case of a pediatric astrocytoma with both MYB rearrangement and EGFR amplification. A 3-year-old boy was found to have a T2 hyperintense, nonenhancing mass in the
left temporal lobe after minor head trauma. Histology showed a diffuse astrocytic tumor with low cell density and bland cytology. Mitotic figures were present, albeit focally, prompting a diagnosis of anaplastic astrocytoma. No necrosis or microvascular proliferation was identified. The Ki-67 labeling index, while generally low, rose to approximately 20%, corresponding to regions of mitotic activity. Interphase fluorescence in situ hybridization analysis showed both rearrangement of MYB in two-thirds of cells and amplification of EGFR in approximately one-quarter of cells. This combination of low- and high-grade molecular features in a pediatric diffuse astrocytoma is so far unique and may
represent the molecular correlate of the rare clinical scenario where a pediatric diffuse astrocytoma, with MYB rearrangement, progresses to high-grade disease.

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