[A Case of Colorectal Cancer with Interstitial Pneumonia during Monotherapy with S-1].

A 76-year-old man with advanced colorectal cancer was started on oral S-1 monotherapy as postoperative chemotherapy. He had dyspnea on exertion, and imaging studies revealed frosted shadows in the bilateral lower lung fields. Transbronchial lung biopsy showed thickening of the alveolar wall, infiltration of inflammatory cells. Based on clinical history and examination results, he was diagnosed interstitial pneumonia with caused by S-1. His respiratory distress on exertion was markedly improved by oral administration of prednisolone(PSL). Thereafter, S-1 medication was not resumed and the patient was followed up on an outpatient basis while the PSL was gradually reduced. According to the S-1 package insert, the frequency of interstitial pneumonia is 0.3%, regardless of the presence or absence of concomitant chemotherapy, so the incidence of S-1 monotherapy is considered to be even lower. In this study, we report a case of colorectal cancer with interstitial pneumonia during monotherapy with S-1, with a review of the literature.