You: "So far you have been right."
Me: I get that all the time. I am very sorry to be right in your mom's case.
You: "Do I tell my mother her survival rate or act as though I don't know? Is ignorance bliss?"
Me: Generally, people don't ask until they are ready to know the truth. Some people never ask, some ask just weeks before they die.
There are many opinions on this. Some feel that not knowing is worse than knowing. At least knowing, one can make better plans for the time on has left. Others feel that not knowing is better, perhaps for very young children.
If you are asking my personal opinion on this very complex issue, I believe strongly in telling the person the truth, but only if they ask for the information - an indication to me they are ready to know. Having said that, I do not think you should be the one to tell her. That is the oncologist's job, let him take care of that.
Cancer patients are just like everyone else and often "shoot the messenger" when horrible news is delivered. You do not want to remind your mother she is dying every time she sees you when you walk in her room, and that is exactly what will happen if you decide to deliver the bad news.
Have the oncologist tell her. If you like, you can be present and your mother can cry on your shoulder and talk it out with you after he leaves the room.
Other opinions on this issue are invited,
-Amnia