Clinical Features and Prognosis of MEK Inhibitor–associated Retinopathy: A Case Series

Purpose: To investigate the clinical characteristics, onset timing, and anatomical and functional outcomes of MEK inhibitor-associated retinopathy (MEKAR) in Korean patients receiving systemic MEK inhibitor therapy.Methods: This retrospective study included 16 patients diagnosed with MEKAR between January 2011 and August 2025.Best-corrected visual acuity (BCVA), central macular thickness (CMT), subfoveal choroidal thickness (CT), and optical coherence tomography (OCT) findings were evaluated at baseline, at MEKAR onset, and at final follow-up.Results: Mean age was 57.8 10.6 years, with a male predominance (68.8%).Colorectal cancer was the most common primary malignancy (56.3%), followed by lung cancer and malignant melanoma (18.7% each).MEKAR developed after a median of 3.3 weeks (IQR, 1.9-4.4weeks) following therapy initiation, and the median time to initial improvement was 2.4 weeks (IQR, 1.3-8.1 weeks).At onset, 62.6% of patients reported ocular symptoms, while 37.4% were asymptomatic.OCT showed reversible retinal changes, most commonly ellipsoid zone thickening (68.8%) and focal subretinal fluid (43.8%), all of which resolved completely.CMT increased transiently at onset compared with baseline (p = 0.002) and normalized at final follow-up (p < 0.001), with no baseline-final difference (p = 0.489).CT remained stable (p = 0.159).BCVA was preserved, with a median of 0.00 logMAR at baseline, onset and final follow-up.Patients undergoing dose modification or interruption showed faster improvement than those continuing therapy (median, 9 vs. 81 days; p = 0.004).One patient showed multiple recurrent episodes, all of which resolved without visual deterioration.Conclusions: MEKAR developed early after treatment initiation and followed a transient, fully reversible course with preserved visual function.Although dose modification accelerated anatomical recovery, long-term outcomes remained favorable even with continued therapy, supporting close monitoring and individualized management rather than routine interruption, particularly in mild or asymptomatic cases.