It depends on how well studied the treatment is. If it's been on the market for 70 years, I'd take the chance. Otherwise, why risk waking up one morning with a tail, or having my arm fall off ;)
Because you are going to die pretty quickly either way if you have terminal cancer. At least if you try a new treatment you could theoretically help other people in the future live for longer, and other people who will get very, very rich. lol
In order for a medication to even begin human testing, you need to show that you've done a ton of lab work to show that a medication works, and that the side effect profile is probably minimal. So, by the time it's offered to you, the risks of the drug having disarming side effects, or of causing you to join the caudal class, are pretty damn minimal.
Let's revisit which medications have harmful side effects a century from now. It's impractical to run studies with thousands of patients, and we haven't had more than half a century of data on most drugs. Not that there's much interest in replicating studies anyways.
I'm not keen to pop a bunch of pills unless there is significant (absolute, not relative) benefit. Drugs are overprescribed in my part of the world, partly because people assume "cuts risk by 50%" must mean "a lot." It might... it might not.