Every cancer is different. There will never be a single drug that deals with all cancers at once. Every cancer originates from a specific organ and even though the cancer is a collective of degenerated cells, it's program will still resemble the program of the original cells.

The nasty thing about cancers is that their development is probabilistic. Some cancers may develop in a more common way for which there are already effective drugs. But you might also get unlucky and get a less typical/less studied form of a cancer and then your treatment options are much worse.