Background: This study exhaustively and historically investigated the status of drug lag for oncology drugs approved in Japan. Methods: We comprehensively investigated oncology drugs approved in Japan between April 2001 and July 2014, using publicly available information. We also examined changes in the status of drug lag between Japan and the United States, as well as factors influencing drug lag. Results: This study included 120 applications for approval of oncology drugs in Japan. The median difference over a 13-year period in the approval date between the United States and Japan was 875 days (29.2 months). This figure peaked in 2002, and showed a tendency to decline gradually each year thereafter. In 2014, the median approval lag was 281 days (9.4 months). Multiple regression analysis identified the following potential factors that reduce drug lag: “Japan’s participation in global clinical trials”; “bridging strategies”; “designation of priority review in Japan”; and “molecularly targeted drugs”. Conclusions: From 2001 to 2014, molecularly targeted drugs emerged as the predominant oncology drug, and the method of development has changed from full development in Japan or bridging strategy to global simultaneous development by Japan’s taking part in global clinical trials. In line with these changes, the drug lag between the United States and Japan has significantly reduced to less than 1 year.
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