S-1, an oral 5-FU prodrug, is an antineoplastic agent used for the treatment of various types of cancer, including cancer of the head and neck. In addition to inflammation, infection, trauma, and iatrogenic causes, nasolacrimal duct obstruction could also be caused by S-1. Herein, we report the case of a patient with nasolacrimal duct obstruction that was suspected to be caused by S-1, and was successfully treated by endoscopic dacryocystorhinostomy (DCR). The patient, a 69-year-old woman, was initiated on treatment with S-1 as adjuvant therapy after resection of breast cancer. Four months later, she developed epiphora, and the lacrimal ducts were intubated with silicone tubes. A year later, she presented with recurrence of epiphora, and was referred to our department. We performed right DCR for nasolacrimal duct obstruction, and the epiphora improved. Although the mechanism of nasolacrimal duct obstruction caused by S-1 has not yet been clarified, otorhinolaryngologists should be aware of this condition.
