Oncogenic KIAA1549-BRAF fusion with activation of the MAPK/ERK pathway in pediatric oligodendrogliomas

Pediatric oligodendrogliomas (pODGs) are rare central nervous system tumors, and comparatively little is known about their molecular pathogenesis. Co-deletion of 1p/19q; and IDH1, CIC, and FUBP1 mutations, which are molecular signatures of adult oligodendrogliomas, are extremely rare in pODGs. In this report, two pODGs, one each of grade II and grade III, were evaluated using clinical, radiological, histopathologic, and follow-up methods. IDH1, TP53, CIC, H3F3A, and BRAF-V600 E mutations were analyzed by Sanger sequencing and immunohistochemical methods, and 1p/19q co-deletion was analyzed by fluorescence in situ hybridization. PDGFRA amplification, BRAF gain, intragenic duplication of FGFR-TKD, and KIAA1549-BRAF fusion (validated by Sanger sequencing) were analyzed by real-time reverse transcription PCR. Notably, both cases showed the oncogenic KIAA1549_Ex15-BRAF_Ex9 fusion transcript. Further, immunohistochemical analysis showed activation of the MAPK/ERK pathway in both of these cases. However, neither 1p/19q co-deletion; IDH1, TP53, CIC, H3F3A, nor BRAF-V600 E mutation; PDGFRA amplification; BRAF gain; nor duplication of FGFR-TKD was identified. Overall, this study highlights that pODGs can harbor the KIAA1549-BRAF fusion with aberrant MAPK/ERK signaling, and there exists an option of targeting these pathways in such patients. These results indicate that pODGs with the KIAA1549-BRAF fusion may represent a subset of this rare tumor that shares molecular and genetic features of pilocytic astrocytomas. These findings will increase our understanding of pODGs and may have clinical implications.