Bristol-Myers Squibb announced today that its pioneering cancer immunotherapy drug Opdivo has been approved for sale in China.

Opdivo targets a protein called PD-1, which is effectively a braking signal in the immune system. Cancer cells are incredibly wily when it comes to evading the body’s own natural defenses, and one of the ways they manage this feat is by tricking the immune system into restraining its own attack dogs. So-called “checkpoint inhibitors” like Opdivo—which is often called by its biological name, nivolumab—essentially remove the biological leash, allowing immune cells to freely attack the cancer predator.

The strategy, along with other immuno-oncology, or IO approaches, has been remarkably effective in a small subset of cancer patients—and has even cured some people with terminal disease. There’s also an inherent danger in IO, as you can imagine. (There are reasons, after all, why the human body has put various limitations and border controls on the immune response.) But that said, from both a clinical point-of-view and a commercial one, there hasn’t been this much excitement over a new class of cancer drugs in a long, long while.

Via Fortune