There's a really good documentary on the evolution of cancer treatments on PBS right now, and one stark fact (that I've noticed elsewhere prior as well) made obvious is just how generic the term cancer is. It's really just any of a million specific types of genetic errors that lead to uncontrolled growth.
Even within the same type of tissue, you can have multiple types of mutations that result in the same effect (uncontrolled growth), hence the different "types" of pancreatic cancer for example. The concept of a "cure" has been reduced down to finding compounds, antibodies, organisms, whatever that can identify and trigger some change only in those cells with that specific genetic mutation. Some of them have external markers and make it a bit easier..
This was the one thing that gives me hope about eventually curing cancers en masse, is that they are essential dumb.. they do not evolve like the common cold, it is a specific mutation that one we find a way to reverse, will have cured it forever.
It was quite amazing watching in the last episode, a woman who had left hospital with a death sentence in stage 4 breast cancer, to be called into a stage 1 herceptin trial and be 100% cured and alive twenty years later. This drug was simply based on antibodies which could recognize the specific markers left by her specific mutation, and 100% cured with no side effects.. We, as humanity, can and will find a way.