Braf Mutation In Chinese Biliary Tract Cancer Patients.

e16678 Background: Biliary tract cancers (BTCs) are a group of relatively rare invasive carcinomas including gallbladder carcinoma (GBC), intrahepatic (ICC), hilar (HCCA), and extrahepatic (ECC) cholangiocarcinoma. In the ROAR basket trial, dabrafenib, a BRAF inhibitor, combined with trametinib, a MEK inhibitor, demonstrated promising efficacy in patients with BTCs with an overall response rate (ORR) of 41% and a favorable safety profile. The frequency of BRAF mutations reported in BTC varies widely, and BRAF V600E mutations have been reported in 0% to 20% of BTCs. However, the frequencies of BRAF mutations in Chinese BTCs are not clear. Methods: A total of 926 BTC patients (203 ECC, 195 GBC, 59 HCCA, and 469 ICC) were included in this study. Formalin-fixed, paraffin-embedded (FFPE) tumor tissues and matching blood samples from these patients were collected and sequenced using next-generation sequencing (NGS) targeting 450 cancer genes. Genomic alterations including single nucleotide variants, insertions and deletions, copy number variations, and fusions were assessed. The testing was carried out by a College of American Pathologists (CAP) accredited and Clinical Laboratory Improvement Amendments (CLIA) certified laboratory. Results: BRAF activating mutations were detected in 5.5% of Chinese BTC patients. There were 5.1% in ICC cases, 8.9% in ECC cases, 5.1% in HCCA cases, and 3.1% in GBC cases. BRAF V600E, the most common hotspot mutation, was detected in ICC and GBC with frequencies of 1.5% and 0.5%, respectively. No BRAF V600E was detected in ECC or HCCA. The top-ranked co-mutation genes with BRAF were TP53 (54%), ARID1A (40%), and SMAD4 (32%). Compared with BRAF wild-type cohort, the frequencies of ARID1A and SMAD4 mutations were significantly higher in patients with BRAF mutations cohort (40% vs 17%, P< 0.001; 32% vs 14%, P< 0.001), while KRAS mutations were mutually exclusive with BRAF mutations. Conclusions: To our knowledge, this is the largest BTCs cohort used to study the characterization of BRAF mutations in the Chinese patients. BRAF mutations occurred in 5.5% of patients, and BRAF V600E in 0.9%. These patients could benefit from treatment with a BRAF inhibitor combined with a MEK inhibitor. Analysis of BRAF V600E should be considered in patients with BTCs, especially in ICC and GBC. Clinical trial information: NCT03892577 .