Is it possible the cure for cancer has already been passed over without us knowing it?

All different: Cancers are all different. No two cancer cells are alike, even within the same patient. So the chance that there will ever be a single cure that will cure all cancer is low. Much more likely that we will get better at testing each cancer to find a cure that is tailored for that particular patient. We may have to do several rounds of this, testing and treating and then retesting.