Retinoic acid is a form of vitamin A that is used to treat and help prevent the recurrence of a variety of cancers, but for some patients the drug is not effective. The reason for this resistance was unclear until this week when researchers demonstrated that a protein known as AEG-1 blocks the effects of retinoic acid in leukemia and liver cancer. Because AEG-1 is overexpressed in nearly every cancer, these findings could impact the care of countless cancer patients.