A novel side effect of mitogen-activated protein kinase inhibitor cobimetinib: Acute corneal decompensation

A 38-year-old man with a diagnosis of BRAF-mutated metastatic melanoma was referred to our clinic. He had been under treatment with 60-mg oral cobimetinib daily for 21 days/7 day off in combination with 960 mg vemurafenib twice daily. The patient had symptoms of blurred vision and photophobia in his right eye. A slit-lamp examination revealed bilateral central corneal stromal opacity and epithelial microcystic edema Involvement was more severe in the right eye compared with the left eye. Fourteen days after the first visit, the patient's symptoms and slit-lamp findings were largely resolved. We suggest that endothelium pump failure was involved in this acute corneal decompensation case similar to the mechanism in retinal pigment epithelium.