[A Case of Serous Retinal Detachment after Encorafenib, Binimetinib, and Cetuximab Treatment for BRAF V600E Mutant Colorectal Cancer].

The patient was a 72-year-old man with a chief complaint of abdominal pain. We performed laparoscopic left hemicolectomy of the colon after descending colon cancer ileus stenting, and postoperative pathology was pT4aN0M0, pStage Ⅱb. In 1.5 years postoperatively, 2 liver metastases and 1 lymph node metastasis were found, and each was resected. Chemotherapy was initiated for multiple lung metastases. Genetic testing was positive for BRAF V600E mutation, and the patient received 8 mFOLFOXIRI plus bevacizumab therapy courses. After 15 5-FU plus LV plus bevacizumab courses, the patient had a brain infarction and lung metastasis reincreased. Chemotherapy was changed to encorafenib plus binimetinib plus cetuximab. On day 2, visual impairment was observed, and serous retinal detachment CTCAE Grade 2 was diagnosed. On day 7, the symptoms improved and one-step dose reduction was resumed. On day 2 of re-treatment, serous retinal detachment recurred and treatment was discontinued. On day 4 of re-treatment, the symptoms improved, another dose reduction was performed, and treatment was resumed. Since subjective MEK inhibitor-induced ocular symptoms are often minor, conducting an interview and early ophthalmologic diagnosis is recommended.