Molecular and clinical characterization of BRAF mutations in pancreatic ductal adenocarcinomas (PDACs).

Abstract

214 Background: The activation of the RAS/RAF/MEK/ERK pathway is critical for the proliferation, survival, and tumorigenesis of PDACs. Oncogenic mutations in KRAS (90%) or BRAF (3%) are recurrent genomic alterations, but their co-occurrence is not well described. We reviewed BRAF alterations and clinical outcomes in consecutive PDAC patients (pts). Methods: Perthera, Inc. deploys an IRB-approved registry that was utilized in partnership with PanCAN’s “Know Your Tumor” program. Perthera uses CAP/CLIA accredited multi-Omic profiling, including next generation DNA sequencing (NGS, Foundation Medicine) and proteomics/immunohistochemistry (Neogenomics Inc. and Caris Life Sciences, Inc.). We used a Fisher's exact test with multiple testing correction to compare frequencies of mutations and protein over-/under-expression between BRAF-mutated (n = 21) and BRAF wild type pts (n = 745). Results: Of 766 pancreatic cancer pts, 21 pts were identified with BRAF mutations. 18 pts were diagnosed with PDAC, 1 pancreatoblastoma, 1 pancreatic acinar cell carcinoma, and 1 mixed acinar neuroendocrine carcinoma. Amongst the 18 PDAC pts with BRAF mutations, nine variations were found: V600E (5/18), BRAF fusion (4/18), N486_P490del (3/18), T310I (1/18), K601N (1/18), G596R (1/18), exon 2-10 deletions & S467L (1/18), equivocal amplification of BRAF (1/18), and a BRAF inframe deletion (1/18). KRAS was mutated in 6% of BRAF mutated PDACs, compared to 94% in BRAF wild type PDACs (p < 0.001). Amongst KRAS wild type PDACs, 53% of CDKN2A mutated pts had BRAF mutations vs. only 15% of CDKN2A wild type cases (p < 0.05). Two BRAF mutated pts from the database were given BRAF inhibitors. A sustained response to the combination dabrafenib and trametinib was observed in a BRAF V600E mutated PDAC pt, while no response was seen in a pt with concurrent KRAS G12A & BRAF K601N mutations who received trametinib. Conclusions: BRAF mutations are significantly and inversely correlated with KRAS alterations. The most common BRAF alteration, V600E mutation, was found to be mutually exclusive with the KRAS mutation. Clinical trials targeting BRAF alterations in KRAS wild type pancreatic cancer appears warranted.