[A case of interstitial pneumonia after S-1 administration for gastric cancer].

An 80-year-old man with no history of thoracic radiotherapy nor interstitial pneumonia was administered S-1 for gastric cancer in June 2007. Twenty-two days after starting S-1, he had dyspnea, and X-rays showed reticular shadows in both lung fields, yielding a diagnosis of interstitial pneumonia. Drug lymphocyte stimulating test (DLST) was positive against S-1. The total dose of S-1 was 2,200 mg to the symptom onset. We immediately started steroid pulse therapy after emergency hospitalization, and it revealed improved condition and he was able to leave the hospital. S-1 administration is becoming frequent because RCTs supported the efficacy of S-1 for gastric cancer. Interstitial pneumonia as a side effect of S-1 is not frequent, but it is necessary to pay attention to dyspnea throughout the duration of administration.