When will cancer be eradicated in humans?
In all seriousness, though, is there really such a thing as "the cancer"? Probably not.
Our current methods of treating it treat it in a piecemeal fashion, targeting one variation or another, but I don't think it's unthinkable that you could managed to target and fix the entire set.
This is why we deal with it piecemeal, because it's the only way we can actually detect it. This isn't a current technical limitation, this is a "we can't solve something before we know the problem" issue due to how cells work. Even in the very long term future where we have bio implants, the best solution we would have are implants being able to seek cancer cells instantly and remove them.
Suppose scanning technology progresses to the point where we can quickly resolve every cell in the human body. Suppose computing technology progresses to the point where we can quickly interpret that scan data and identify which areas are normal and which areas are tumorous growths that shouldn't exist. Suppose surgical(/point application of energy) technology progresses to the point where we can destroy any individual cell without collateral damage.
I believe at that point we could solve the entire set of conditions called cancer (but maybe not all disease, maybe some forms of dementia still evade us for instance).
I'm not criticizing the current approach by calling it piecemeal. It's what we know how to do, doing it saves lives, of course we should do it. I'm just saying that cancer is a meaningfully label, and it's conceivable that at some point we can solve it, all of it.