Pathological Complete Response after Beacon Regimen for Recurrent Colorectal Cancer of BRAF-Mutant—Report of a Case—

Abstract

A 78-year-old woman underwent right hemicolectomy for cancer in the hepatic flexure of the transverse colon. Histologically, it was poorly differentiated adenocarcinoma, RAS mutation-negative, BRAF mutation-positive, and MSI-H. Since the resection margin was positive, mFOLFOX6 was performed from 4 weeks after the operation. After completion of 3 courses, a contrast-enhanced CT scan revealed a recurrence of 50 mm in size on the ventral side of the pancreatic head and 42 mm in size on the ventral side of the right greater psoas muscle, involving the ureter. He had a history of Basedow disease. Considering a risk of causing thyrotoxicosis as an immune-related adverse event of pembrolizumab, encorafenib + binimetinib + cetuximab therapy was started as second-line therapy. After 9 courses, the tumor disappeared leaving only a soft shadow, and a complete response was obtained on imaging. Meanwhile the regimen became unsustainable due to the infusion reaction. Since the curative resection was judged to be possible, pancreatoduodenectomy and right ureter combined resection and reconstruction were performed, and no tumor cells were found histopathologically. This is the first report in Japan of a complete pathological response to chemotherapy for BRAF-mutant colorectal cancer.