BRAF fusion in lung cancer.

e21598 Background: BRAF was a part of RAS/MAPK pathway, which regulated the proliferation, differentiation, migration, and apoptosis of cells. BRAF V600E was a potential treatment target for non-small cell lung cancer and other tumors. While BRAF fusion was rare in lung cancer. Here we focus on BRAF fusion in lung cancer. Methods: We retrospectively reviewed next-generation sequencing (NGS) results of lung cancers, with or without treatment history. The samples were subjected to NGS using 59 or 1021-gene panel, which enables simultaneously assess snv, indel, rearrangements and cnv variations. Patients with BRAF fusion were collected and used to analysis. Results: We found eighteen lung cancers have BRAF fusion from about twelve thousand patients, 13 are females. The median age at diagnosis was 47-year old (range 28 to 70). Tested samples included 13 tissues, 5 plasma, and 2 pleural effusion. BRAF fusion could occur in different stage, 12 stage Ⅳ and 1 stage Ⅰ, other were unknown. There were 14 lung adenocarcinoma, 1 squamous cell carcinoma and 1 adenosquamous carcinoma, other two patients were unknown. The partner genes of BRAF fusion were distinctly among the patient, TRIM24 was relatively common. The median tumor mutation burden (TMB) was 4.8muts/Mb (range 0 to 15.4), with low TMB-H frequency (10.5%, defined 9 as cutoff value). Seven patients had no system treatment history, and 1 had concurrent EGFR L858R mutation. Nine patients received EGFR-TKI therapy, 1 received ALK-TKI therapy, and 1 received chemotherapy. Among the EGFR-TKI treated patients, 7 received first and third generation TKI sequential therapy, the median TTD (time to discontinue) of TKIs was 26 months (range 17 to 46). The EGFR mutation still exist when EGFR-TKIs resistance, included EGFR primary mutation, T790M, and C797S, concurrent with BRAF fusion. Except for BRAF fusion, there also had other complex resistance mechanism occurred, like HER2 mutation, KRAS mutation, etc. Conclusions: BRAF fusion had low frequency in lung cancer and occurred at different stage during disease development. BRAF inhibitors maybe a potential strategy for BRAF fusion lung cancers. As TKIs resistance mechanism, BRAF fusion is a huge clinical challenge, indicate the importance of further research.