I see it a bit differently, if you can figure out both all of the functional relationships in our bodies and devise a mechanism to precisely drive any and all of them, not only will you 'cure cancer' but you will be able to cure any other disease or ailment that is expressed as an undesirable functioning of that system.

I don't know if you can do that with $20B but I feel these days that its more likely to occur rather than the opposite (which is to discover some underlying uncertainty principle that would prevent directing cellular action in a predefined way.)