I imagine that our descendants will have a certain kind empathetic pity on us for not knowing this for certain in the same way we look back on people not knowing what atoms were.
Your assuming our descendants aren't living in a post apocalyptic dystopia where civilized society is little more than a fairytale. We may seem like gods to them. And it may be much closer than people expect, perhaps hundreds not thousands of years.
As I understand it, almost every cancer treatment consists in gradually killing the patient in such a way that the cancer dies, hopefully before the healthy tissue, and then nursing the patient back to health. If we ever find a better approach, people will be utterly horrified at chemo and radiation therapy.
That is true for cancers without targeted therapies. But cancers such as CML, breast cancer, melanoma, etc, all now have targeted therapies against specific molecules (often tyrosine kinases).
While alkylating agents, etc, are still widely used, I think it's fair to say that the future that you have described is the present. We have the better approach, and now it's a matter of aggressively pursuing it (which is also happening).
Some earlier versions of mankind had great knowledge too and not all of that has been preserved for us. Try to rebuild the Pyramids of Gizeh today for example. Do we today know exactly how this stuff worked?
It's pretty easy for us to rebuild the pyramids today, but what's hard is trying to do so with the same level of technology the Egyptians probably had at the time, which makes them wonders of the world instead of just another easy-to-make mudhut.
