Abstract
We experienced a case of bilateral corneal thinning during the oral taking of S-1, a combination anti-cancer drug of tegafur, gimeracil, and oteracil-potassium. A 69-year-old man was prescribed oral S-1 for the treatment of duodenal papilla adenocarcinoma and intraductal papillary mucinous neoplasm. However, he developed a decrease in visual acuity in both eyes after three cycles of S-1 oral taking, and ophthalmic examination revealed corneal thinning exceeding 100 µm and an increase in high-order irregularity of cornea in both eyes. After one month after discontinuation of S-1, his visual acuity and corneal thickness returned to its previous levels. Besides corneal ulcers and perforations, corneal thinning can be recognized as a potential corneal side effect necessitating monitoring during S-1 treatment.