They must have some kind of lab results to justify a consult with an oncologist, maybe they got some endometrial cells from the pap smear that show pre-cancerous cells? That is what happened to me, my lab results showed precancerous changes, but not actual cancer, therefore, they sent me along to the oncologist because they wanted him to supervise my case and be in the loop on any developments in case it turned out that it became cancer and there would be no delay to get him on my case immediately. Please keep your head up and don't panic, but a very thickened lining needs to be thoroughly investigated or you will never have any peace about it. Try to think about it in terms of getting more information so that you can take better care of yourself whatever happens in your case.
Also, I was told that in women that show pre-cancerous changes, there are a certain percentage of those who turn out to actually already have cancer that they can only detect if the uterus and/or lymph nodes get removed. I had a laparoscopy where they went in with a scope and looked at the outer surface of my uterus, ovaries, and abdomen and they saw nothing cancerous-looking in there. I thought, GREAT!, but then was told that it is possible that it could invisibly spread to lymph nodes and still look normal on the outside.
These female parts are a little too much fun sometimes, aren't they?
Take care of yourself and good luck!