With your doctor not listening and you thinking you may have sarcoma, you will only know after seeing a cancer specialist. If they suspect a sarcoma, a MRI and or CT will normally be ordered of the suspected area. If test results are positive, a biopsy will be ordered. Then you will know. Sarcomas are usually located in area of soft tissues like arms, legs, abdomens, lungs, etc. Lots of information can be found on Mayo Clinic website.
I am a 3 cancer survivor. All different, all bad. Latest was undifferentiated pleomorphic sarcoma (UPS) of the front right thigh removed at Mayo, Rochester 04/2020. The best thing you can do is have and maintain a good attitude. Attitude will get you through the diagnosis, possible treatment and any recovery from whatever lies ahead of you. And know that Mayo, in my opinion, is the place to go. Best wishes to you