Many kinds of tumors make an immune system-suppressing protein that is linked to more extensive disease and reduced survival. Now, a completed phase I trial suggests that an experimental drug that inhibits this protein could help people with a range of cancers that have not responded to other treatments. The protein is called oral indoleamine dioxygenase-1 (IDO1), and the drug that inhibits it is called INCB024360. The trial showed that this drug kept tumors from growing in 30% of the 52 people treated, half of whom had colorectal cancer, which has generally resisted immunotherapy. Moreover, this new drug had manageable side-effects. These findings were presented at the 2013 meeting of the American Society of Clinical Oncology. Now, a Phase I/II trial is underway to test treating melanoma with INCB024360, both alone and in combination with ipilimumab, another immunotherapy.