Summary

Pulmonary injuries due to S-1 have been reported, and these reports have shown an increase in lung cancer following the increased usage of S-1 in treating lung cancer. We report the first case of lung injury due to S-1 in combination with pneumocystis pneumonia (PCP), because the radiological findings and clinical courses were compatible with S-1-induced lung injury combined with PCP. We should consider that S-1 might induce lung injuries which might occur with PCP, especially with a history of drug-induced or radiation-induced lung injuries.