A hidden vitamin A signal may be helping cancers escape the immune system—and scientists just found a way to turn it off. Credit: Researchers at the Princeton University Branch of the Ludwig Institute for Cancer Research have uncovered new ways a vitamin A-derived molecule can interfere with the immune system's ability to fight cancer. The molecule, known as all-trans retinoic acid, was found to weaken natural anti-cancer immune responses and, under certain conditions, reduce the effectiveness