It’s a violent world in there. Every day, billions of cells in our bodies are marked for death, then hunted down and killed. Billions more commit suicide.

It might all seem terribly grim and frightening were it not for the fact that all this violence is what keeps us alive. The killing is done by our immune system, and the suicides eliminate normal cells that have become diseased or are no longer needed. What’s more, those suicidal cells may hold the key to powerful new cancer treatments.

Cancer researcher Dr. Tak Mak has taken a special interest in the immune system for most of his professional life. In fact, it was Dr. Mak who, in 1984, first described the mechanism by which receptors on the immune system’s “T-cells” identify invading pathogens like viruses.

These days, however, Dr. Mak is focused on how and why our own cells commit suicide. All healthy cells carry a self-destruct code that’s triggered automatically when the cell becomes diseased or is no longer needed. If the code fails to execute, surrounding cells or agents of the immune system can also carry out the death sentence. The process is known as apoptosis or “programmed cell death,” and results in the natural destruction of 50 to 70 billion cells a day in our bodies.

Most cancers result from a failure of apoptosis, allowing unhealthy cells to survive and multiply into tumours. Dr. Mak characterizes these cells as “mis-wired,” and one of his key research initiatives is aimed at understanding how it happens. “If you find how these cells are mis-wired,” he says, “you can send in a drug to tackle that.” These “sharp-shooter” drugs—a term that seems apt for the violent world of the cell—repair the failed cell-suicide mechanisms that allow cancers to proliferate. The approach avoids what Dr. Mak refers to as the “collateral damage” of chemotherapy, which kills healthy cells as well as cancerous ones.

It’s not as easy as it may sound, however. Understanding how apoptosis works, and how it fails, is a daunting task. “We start teasing apart cancer cells,” explains Dr. Mak, “and to our dismay, we find that every patient is mis-wired differently. So what we try to do is to look for the kinds of mis-wiring problems that recur most often and go after those.”

Despite the complexities involved, sharpshooter drugs are starting to appear. Several forms of leukemia can now be completely cured with this approach. And Dr. Mak refuses to rule out a breakthrough in understanding apoptosis that could lead to a revolution in drug design and treatment. “We could get lucky,” he says. “But by and large, we make progress one step at a time.”