The challenge is that if you stimulate your immune system, it might get over-stimulated. And it might actually start causing harm to normal cells in your body. So we have to work a balance between attacking the cancer and not attacking yourself.

We are living through a remarkable time where we're translating this investment that we've made in cancer science to new treatments. And they're benefiting a large number of people and they will benefit many more in the years to come.

We certainly do have to be realistic about where we stand. It is the case that cancer is the second-leading cause of deaths in the U.S., in fact, in nearly half the states it's the leading cause of death. And we have a ways to go.

The challenge is that if you stimulate your immune system, it might get over-stimulated. And it might actually start causing harm to normal cells in your body. So we have to work a balance between attacking the cancer and not attacking yourself.

Cancer is complex and therefore there is not a one-size-fits-all solution.

Actually, as cancers develop in an individual patient, an individual cancer cell might be different - a little bit different - from the cell that's sitting right next to it. And so there's heterogeneity, we call it. It makes the problem that much harder.