Ophthalmic Toxicities in BEACON Triplet Therapy for BRAF V600E-Mutant Colorectal Cancer: A Case Series

The BEACON regimen, comprising cetuximab, encorafenib, and binimetinib, is a critical treatment for BRAF-mutant metastatic colorectal cancer (mCRC). While effective, this regimen may be associated with a high frequency of serous retinal detachment (SRD) as an ocular toxicity, which is a less recognized risk in colorectal cancer. Here, we report three patients with mCRC who developed SRD shortly after starting BEACON therapy. Each patient experienced acute visual disturbances, and optical coherence tomography (OCT) confirmed SRD without other retinal abnormalities. Temporary discontinuation of therapy improved the OCT findings in all patients. Two patients resumed treatment with a doublet regimen (excluding binimetinib) and maintained stable vision without irreversible damage. The third patient continued binimetinib with an adjusted dosing schedule of 1 week administration and 1 week off, with no ocular toxicity; the other two drugs were continued. None of the patients experienced permanent vision impairment. These cases highlight the importance of early recognition and proactive management of ocular toxicity in patients receiving BEACON therapy. Regular ophthalmological monitoring and appropriate dose adjustments are essential to prevent visual damage while maintaining treatment efficacy.