One special area to consider is late side effects. Some cancer drugs can cause a second cancer years later, and some can also cause serious damage to the heart that may not show up for years. You have to put these things in perspective though. In some cases though, different treatment options may have different chances of causing serious damage. You may be able to find a safer treatment by researching the options, though, of course, there's no guarantee of that either.
Some treatments are much safer in the hands of a real expert.
Perhaps there is someone who is particularly expert in a delicate surgery who can do it more safely than most other doctors. If you are facing a highly toxic treatment that will only extend your life a short time at best, you may well decide it isn't worth it. As a 32 year old patient with a small, but real, chance to beat terminal cancer, I was willing to endure whatever it took to get that chance. No matter what. It's important to get the facts on just how miserable the side effects are going to be.