I am not a nurse or medical professional, but I just wanted to comment to say that sometimes when people get a diagnosis like that, they may not hear things accurately.

I had thyroid cancer, a comparatively mild form of cancer and this is one of the reasons I asked my mum to come to some of my appointments with me (the main reason was I didn't want to have to go home and give her bad news), because afterwards you start thinking over and over what they said and start wondering, "did they really mean to say...?" "was he trying to imply x without scaring me too much?" etc. So it is quite possible the doctor said something like "we saw something very concerning" or "this is a serious diagnosis" and she heard "the worst they've ever seen."

Obviously, you know your MIL and I don't, but I don't think the only options are "the doctor said those exact words" or "she is not telling the full truth and is deliberately adding to it." The latter is possible, but unless you have some reason to believe her that kind of person, I'd say that panicking and interpreting her doctor's words in the worst possible light is probably more possible (if she does have a history of lying or manipulation, then that changes things a bit).

The stress of the whole situation could also be affecting her appetite.

Again, I have no medical knowledge and don't know your MIL, so I am not saying this is the case. You know her better and are far better placed to say whether losing her appetite is a likely response to stress for her and so on. Just saying it is a possible explanation.

Thank you. I hope you on your way to a full recovery. Thank you for taking the time to reply.  I totally understand but she does like a tall tail I think I am just worried that a doctor said something that till all the tests are done they cant fully understand. But you maybe right and she has just heard all the bad. Only time will tell we will continue to support her no matter what.