Pilocytic astrocytoma harboring a novel GNAI3‐BRAF fusion

Pilocytic astrocytoma (PA), a central nervous system (CNS) World Health Organization grade 1 tumor, is mainly seen in children or young adults aged 5–19. Surgical resection often provides excellent outcomes, but residual tumors may still remain. This low‐grade tumor is well recognized for its classic radiological and morphological features; however, some unique molecular findings have been unveiled by the application of next‐generation sequencing (NGS). Among the genetic abnormalities identified in this low‐grade tumor, increasing evidence indicates that BRAF alterations, especially BRAF fusions, play an essential role in PA tumorigenesis. Among the several fusion partner genes identified in PAs, KIAA1549‐BRAF fusion is notably the most common detectable genetic alteration, especially in the cerebellar PAs. Here, we report a case of a young adult patient with a large, right‐sided posterior fossa cerebellar and cerebellopontine angle region mass consistent with a PA. Of note, NGS detected a novel GNAI3‐BRAF fusion, which results in an in‐frame fusion protein containing the kinase domain of BRAF . This finding expands the knowledge of BRAF fusions in the tumorigenesis of PAs, provides an additional molecular signature for diagnosis, and a target for future therapy.