BRAF fusions in pediatric histiocytic neoplasms define distinct
therapeutic responsiveness to RAF paradox breakers
Abstract
Pediatric histiocytic neoplasms are hematopoietic disorders frequently
driven by the BRAF-V600E mutation. Here we identified two BRAF gene
fusions (novel MTAP-BRAF and MS4A6A-BRAF) in two aggressive histiocytic
neoplasms. In contrast to previously described BRAF fusions, MTAP-BRAF
and MS4A6A-BRAF do not respond to the paradox breaker RAF inhibitor
(RAFi) PLX8394 due to stable fusion dimerization mediated by the
N-terminal fusion partners. This highlights a significant and clinically
relevant shift from the current dogma that BRAF-fusions respond
similarly to BRAF-inhibitors. As an alternative, we show suppression of
fusion-driven oncogenic growth with the pan-RAFi LY3009120 and MEK
inhibition.