Wednesday, September 21, 2016

CAP16 Abstract Highlights - BRAF Mutational Status in Desmoplastic Infantile Astrocytoma/Ganglioglioma

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.

Ashley Greer and colleagues at the University of Colorado in Poster #194 discuss the BRAF mutational status of DIA/DIG.

Context: Desmoplastic infantile astrocytoma/gangliogliomas (DIA/DIGs) are rare, massively cystic tumors usually found in superficial cerebral hemispheres. They are characterized by prominent desmoplastic stroma, interspersed neoplastic astrocytes, and fewer, if any, neoplastic ganglion cells. While BRAF mutation is found in up to 50% of pediatric gangliogliomas, 2 recent studies found it was rare in DIA/DIGs. We sought to assess BRAF mutation in our DIA/DIGs.

Design: Review of departmental files from 2000–2016 was performed to identify DIA/DIGs, with review of clinical outcome, neuroimaging features, immunohistochemistry (IHC) for astrocytic and neuronal markers, and BRAF VE1. BRAF mutational assessment was undertaken in IHC+/equivocal cases, with additional next generation sequencing whenever possible.

Results: All 6 cases were cerebral-hemispheric, with overlapping neuroimaging features (Figure 76, A and C) and favorable clinical outcomes, although histologic differences were noted. Five of 6 tumors contained a predominantly neoplastic astrocytic population (Figure 76, B), while DIA/DIG from the oldest child (12 months) showed exceptionally large nodules of neoplastic ganglion cells (Figure 76, D). This was the only case to show either BRAF VE1 IHC+ and/or mutation (rare c1799_1800TG.AT; p V600D). Next-generation sequencing on this case, and a comparison astrocytic-dominant DIA/DIG, showed only mutation in BRAF, and not in 26 other commonly mutated genes.

Conclusions: Five of 6 classic DIA/DIGs were negative for BRAF mutation. Previous publications found mutation in 2 of 18 and 1 of 14 cases; 2 of 3 reportedly mutated cases were unusual in that they were in atypical anatomic locations (suprasellar, fourth ventricle), and 1 was in an older child (24-month-old). DIA/DIGs with unusual features may be more likely to show BRAF mutation similar to ganglioglioma.

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