INTRODUCTION
NSCLC, tumor, Lung cancer, gastrointestinal, head and neck,, biliary tract cancers, gastrointestinal toxicity, squamous cell carcinoma, deaths
TUMOR, BILIARY TRACT CANCER, LUNG CANCER, ADENOCARCINOMA, NSCLC, SQUAMOUS CELL CARCINOMA
Lung cancer is one of the leading causes of cancer‐related deaths both in Japan and worldwide.For patients with NSCLC previously treated with platinum‐doublet chemotherapy, single‐agent chemotherapy, such as pemetrexed and docetaxel, is recommended. However, in terms of efficacy, pemetrexed is not recommended for patients with squamous cell carcinoma.S‐1 is a novel oral fluoropyrimidine agent consisting of tegafur, 5‐chloro‐2, 4‐dihydroxypyridine (CDHP), and potassium oxonate at a molar ratio of 1:0.4:1. Tegafur is a prodrug of 5‐fluorouracil (5‐FU), whereas CDHP inhibits dihydropyrimidine dehydrogenase, the enzyme responsible for degrading 5‐FU. Compared with tegafur alone, tegafur plus CDHP increases 5‐FU concentration in the serum and tumor tissue. Potassium oxonate is expected to alleviate the gastrointestinal toxicity of tegafur. S‐1 is commonly used for the treatment of gastrointestinal, head and neck, NSCLC, breast, pancreatic, and biliary tract cancers. In a phase II trialIrinotecan (CPT‐11), an inhibitor of DNA topoisomerase I, is used in the treatment of NSCLC and has a different mechanism of antitumor activity than that of S‐1. Two randomized phase III trialsIt has been suggested that thymidylate synthase (TS) expression levels in squamous cell carcinoma are higher than those in adenocarcinoma,