Abstract 5775: Landscape of BRAF and RAF1 fusions identified by next-generation sequencing in a Chinese multi-cancer retrospective analysis
Authors: Li Tao , Zhang Xin , Niu Yanling , Ma Tonghui 
Published: June 2022

Abstract
Background: The RAF family includes three members, ARAF, BRAF, and RAF1/CRAF. These kinases function downstream of RAS as part of the MAPK (RAF-MEK-ERK) signaling cascade. The BRAF gene is mutated in ∼7% of cancers, whereas ARAF and RAF1 mutations are rare. Gene fusions in BRAF or RAF1 fusions, which activate the MAPK pathway, can be oncogenic drivers in a variety of cancer types and represent potential targets for targeted therapy. Here we focused on the prevalence of BRAF and RAF1 fusions in a multi-cancer cohort for patients (pts) whom might benefit from MEK/RAF inhibitors in clinical development.
Methods: Genomic profiling was performed on samples from 29,102 lung cancer pts, 676 melanoma pts, 392 colorectal cancer pts, 1,463 gastric cancer pts, 1,014 sarcoma pts, 1,079 liver cancer pts, 215 gallbladder carcinoma pts, 297 ovarian cancer pts, 46 tongue cancer pts, 62 thymic carcinoma pts, 6 hemangioma pts, and 890 pancreatic cancer pts using next-generation sequencing (NGS), which covers all exons of BRAF and RAF1. The fusion patterns were analyzed.
Results: A total of 5 RAF1 and 114 BRAF fusions were identified in approximately 0.34% (120/35,242) of the patients in this Chinese multi-cancer cohort. The positive rates of RAF1 fusions were 0.0034% (1/29,102) in lung cancer pts, 0.44% (3/676) in melanoma pts, and 0.10% (1/1,014) in sarcoma pts. The fusion partners of RAF1 were LYRM4 in lung cancer, LMCD1 and USP20 in melanoma, and FMR1 in sarcoma. RAF1 fusions involving the intact in-frame RAF1 kinase domain were LYRM4-RAF1, LMCD1-RAF1, and USP20-RAF1, which might be targeted with MEK/RAF inhibitors. The BRAF fusion-positive rates were 0.27% (80/29,102) in lung cancer pts, 1.18% (8/676) in melanoma pts, 2.81% (11/392) in colorectal cancer pts, 0.41% (6/1,463) in gastric cancer pts, 0.20% (2/1,014) in sarcoma pts, 0.19% (2/1,079) in liver cancer pts, 0.47% (1/215) in gallbladder carcinoma pts, 0.34% (1/297) in ovarian cancer pts, 2.17% (1/46) in tongue cancer pts, 1.61% (1/62) in thymic carcinoma pts, 16.67% (1/6) in hemangioma pts, and 0.11% (1/890) in pancreatic cancer pts. The most common 5’partners of BRAF were TRIM24 (4 cases) and SND1 (3 cases). Whereas the most common 3’partners of BRAF were BAIAP2L1 (5 cases) and TRIM24 (4 cases). Furthermore, 57 BRAF fusions contained intact BRAF kinase domain and nearly half of BRAF fusion-positive patients might be sensitive to MEK inhibitor. The most frequent location of the breakpoints occurred in intron 8 of the BRAF gene, followed by intron 7. However, the sensitivity of these fusions to MEK/RAF inhibitors in different cancers needs to be further studied.
Conclusions: This study revealed the molecular features of BRAF and RAF1 rearrangements in Chinese cancer patients, which could help to identify therapeutic targets and personalize therapy management, leading to improved patient outcomes.
Citation Format: Tao Li, Xin Zhang, Yanling Niu, Tonghui Ma. Landscape of BRAF and RAF1 fusions identified by next-generation sequencing in a Chinese multi-cancer retrospective analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5775.