Our immune systems can destroy cancer - but the immune system grows less effective with age, and sometimes it fails in this task. That "sometimes" is enough to kill a quarter of humanity, the fraction of us who die from cancer. Researchers are closing in on the mechanisms that separate success from failure, however, and in the years ahead will be able to tune our immune systems to destroy cancer nearly 100% of the time: "A specific type of T helper cell awakens the immune system to the stealthy threat of cancer and triggers an attack of killer T cells custom-made to destroy the tumors ... The role of Th17, one of only four known types of T helper cell, opens a possible avenue for overcoming cancer's ability to suppress or hide from the body's immune system ... While there is much work to be done, these preclinical findings imply the possibility of taking a patient's Th17 cells, expanding them in the lab, and then re-infusing them as treatment ... Development of a vaccine to stimulate Th17 cells would be another possible application."