You've got to get away from the idea cancer is a disease to be cured. It's not a disease really. The cancer cell is your own body, your own cells, just misbehaving and going a bit wrong, and you don't have to cure cancer. You don't have to get rid of all those cells. Most people have cancer cells swirling around inside them all the time and mostly they don't do any harm, so what we want to do is prevent the cancer from gaining control. We just want to keep it in check for long enough that people die of something else.
