Activating NRF1-BRAF and ATG7-RAF1 fusions in anaplastic pleomorphic xanthoastrocytoma without BRAF p.V600E mutation

Excerpt

Pleomorphic xanthoastrocytoma (PXA, WHO grade II) and anaplastic PXA (WHO grade III) are astrocytic neoplasms that commonly harbor an activating mutation in BRAF (p.V600E, c.1799T>A) [4, 7], driving activation of the mitogen-activated protein kinase (MAPK) signaling pathway. Currently, PXA is diagnosed based solely on histopathologic features. Yet recent reports based on DNA methylation suggest anaplastic PXA-like tumors can masquerade as glioblastoma (GBM) [3, 1]. Importantly these PXA-like tumors were associated with a more favorable prognosis than GBM and included both BRAF p.V600E mutant and non-mutant tumors in approximately equal proportions [3]. These findings suggest both histologic analysis and determination of BRAF p.V600E mutation status may not capture all tumors with the biologic behavior of anaplastic PXA. Here, we report on the identification of in-frame genomic rearrangements predicted to result in NRF1-BRAF and ATG7-RAF1, constitutively active kinase fusions, in two anaplastic PXA without BRAF p.V600E mutation. …