Case Report: Molecular diagnostics and clinical courses of two adult spinal pilocytic astrocytoma long-term survivors with GTF2I::BRAF fusion.

Introduction: Pilocytic astrocytomas are driven by BRAF and mitogen-activated protein kinase (MAPK) alterations, typically KIAA1549::BRAF fusions. A rare GTF2I::BRAF fusion has been described, but little is known about these cases. Case report: Here, we report two cases with GTF2I::BRAF fusions. Case 1 is a 36-year-old man initially diagnosed with myxopapillary ependymoma at the conus medullaris with three recurrences over 23 years requiring two surgeries, three rounds of radiation therapy, and one round of lapatinib/temozolomide. A distant disease focus in T3/T4 was sampled and tested with modern diagnostic techniques revealing a pilocytic astrocytoma on histology and methylation profiling. The patient has subsequently had stable clinical and radiographic findings. Case 2 is another 36-year-old man initially diagnosed with meningitis and later neurosarcoid who underwent biopsy after 12 years when his spinal leptomeningeal disease continued to progress and an intraventricular non-enhancing nodule emerged as a separate focus. Sampling of the leptomeningeal disease led to a diagnosis of pilocytic astrocytoma by histology and a divergent methylation profile. The patient has remained neurologically stable under radiographic surveillance without any intervention. Results: Radiographic, histological, and molecular data are presented for both cases and compared against the only other reported GTF2I::BRAF CNS case, as well as canonical versions of pilocytic astrocytoma. Conclusion: To our knowledge, this is only the second case series highlighting a unique GTF2I::BRAF fusion and the first to describe it in adults in a spinal location. The manuscript contributes documentation of a rare fusion and tumor presentation to guide clinicians and potential research avenues.