Bilateral Serous Retinal Detachment Associated with a Mitogen-activated Protein Kinase Kinase Inhibitor in a Patient with BRAF-mutant Colorectal Cancer

We herein report a 73-year-old woman with BRAF V600E-mutated colon cancer treated with encorafenib plus cetuximab with binimetinib as standard salvage therapy for patients with advanced colorectal cancer. She developed bilateral serous retinal detachment the next day, and the regimen was discontinued, resulting in complete resolution by the third day. Doublet therapy without binimetinib was initiated along with a weekly ophthalmologic examination for 10 weeks without recurrence of retinal detachment. Thus, binimetinib was presumed to have been the cause of the retinal detachment. This clinical course suggests the need for close monitoring of patients for vision impairment and close collaboration with ophthalmologists.