We have an immune system capable of dealing to most things, it just needs enough vitamin C to allow it to function (heat treatment effectively destroys vitamin C). Increasing the amount of Vit C in the diet of most people would be the single greatest disease prevention measure possible – of that I have no reasonable doubt left (having cured myself of “terminal melanoma” after being sent home “palliative care only”). Minimum quantities of 2g per day, seem to be indicated for most people. I’m on about 20g per day, and was up to 100g per day when trying to rid myself of tumours.
The next greatest advance is highly unlikely to occur with single drugs, or even groups of them, but rather with very smart nanotechnology programmed to work in close harmony with, and supplemental to, our native immune system. Drug delivery may form part of that mechanism, and it is likely to be drugs targeted to specific cells.