[A Case of BRAF Mutant Cecal Cancer Treated with Encorafenib, Binimetinib, and Cetuximab Triple Therapy].

A Japanese woman in her early 70's presented to our hospital with abdominal pain and nausea. Abdominal computed tomography showed irregular wall thickening of the ileocecal region and small intestine dilatation. Colonoscopy revealed a tumor lesion at the ileocecal valve and adenocarcinoma was detected in the biopsy specimen. Accordingly, the diagnosis was cecal cancer and bowel obstruction. Right hemicolectomy was performed as palliative surgery, and laparotomy findings revealed peritoneal dissemination. The final staging was pT4a, pN2b, pM1c, pStage Ⅳc, harboring a BRAFV600E mutation. Rapid postoperative tumor progression occurred, leading to multiple liver metastases and ascites. Encorafenib, binimetinib, and cetuximab triple therapy was started as a second line regimen. The therapy was extremely effective. CA19-9 level decreased to within normal range, and the liver tumor size was visibly diminished. After receiving treatment for 2 months in outpatient care, she had to discontinue the treatment due to carcinomatous peritonitis. Unfortunately, she died 6 months after initial diagnosis. BRAF-mutated colon cancer is associated with poor prognosis. In Japan, encorafenib, binimetinib, and cetuximab triple therapy is a new BRAF targeting regimen approved in 2020. We report this clinical course in hopes of eventually achieving better outcomes for patients with this aggressive disease.