You probably know this, but just to be clear, things can light up on a PET scan and not be cancer. A PET scan specifically shows things that have a high metabolism. Cancer has a high metabolism so it shows up but other things that have a high metabolism also show up.
My PET scan showed my lung cancer and a couple lymph nodes that had cancer but it also showed a tumor in my right sinus of all places. This was removed surgically and the pathology showed without a doubt that it was not cancer. It just happened to have a high metabolism.