In addition, for IDO and TDO inhibitors that do have tolerable safety profiles, it is hoped that the issue of tumor‐acquired resistance may be overcome by combinatorial administration of these inhibitors or the use of dual‐targeting IDO/TDO inhibitors, both of which might prevent tumor escape from more selective drugs that fail to inhibit an alternative tryptophan‐catabolizing pathway when administered as single agents. The gene discussed is IDO1; the disease is neoplasm.