Turn Off the IDO: Will Clinical Trials Be Successful?

Indoleamine 2,3-dioxygenase (IDO) is overexpressed in many human cancers and is believed to play a role in tumor immune evasion, but a requirement for IDO in tumor progression has not been formally shown. The study by Smith and colleagues in this issue of Cancer Discovery provides genetic evidence for the importance of IDO in tumorigenesis, which supports the use of IDO inhibitors in clinical trials in humans. Cancer Discov; 2(8); 673-5. (C) 2012 AACR. Commentary on Smith et al., p. 722 (7).