There has been an explosion in neat novel anti-cancer agents that are basically synthetic antibodies that target specific cell receptors on cancer cells, exorbitantly expensive for the most part of course. Patients generally aren't on the same cancer drug for years at a time. It's more profitable to try to discover some new drug that actually cures them so you are selling the $400,000 first choice drug whenever a patient has melanoma with a certain gene mutation for example. You need to "win" outright and kill essentially all of the cancer cells so the patient goes into remission; if the tumor starts to resist the drug or develops a bunch of new mutations, the oncologist will need to switch to something else if your drug is clearly not working.

The real pharmaceutical scam is meds for things like GERD and hypertension where you find a new drug that is debatably 2% better, market it directly to patients on TV, then charge Medicare 10 times as much as the old drug while 20% of the US population takes it.