Rare BRAF gene fusions in metastatic early-onset colon cancer: A case report

Gene fusions offer new therapeutic options for patients with metastatic colon cancer (CC). <i>BRAF</i> gene fusions are infrequent somatic mutations found in CC with prognostic and promising targeted therapies. CC diagnosed before the age of 50 was regarded as early-onset CC (EOCC). The incidence of EOCC is increasing, yet there is a clear unmet need to improve the management of EOCC. Herein, we selectively reported a case of metastatic EOCC with rare <i>BRAF</i> gene fusions. The right-sided tumors were radically resected. Next-generation sequencing (NGS) was performed on formalin-fixed paraffin-embedded tissues to eliminate gene variations. Histologically, the colonic hepatic flexure showed focal mucinous adenocarcinoma changes along with high-grade intraepithelial neoplasia. The results of histopathological examination belonged to pT1bN1bM0 ⅢA stage. Targeted DNA sequencing revealed <i>AGAP3::BRAF</i> (A10;B9) fusion and <i>BRAF::AGAP3</i> (B8;A11) fusion were simultaneously detected in this case. Microsatellite instability-high (MSI-H) and <i>RAS/BRAF</i> ^<i>V600E</i> mutations were not detected. During a limited 1.5-year follow-up period, neither a confirmed local recurrence nor a distant organ metastasis occurred in this case. We propose that <i>BRAF</i> fusion variations can occur in metastatic EOCC.