I've never heard of a doctor notifying a patient that you "might" have cancer though a letter. All test results are usually given in the office, especially something as serious as cancer. Thats just awful that he did that to you - especially since its not confirmed; making you worry over something that might not even be.
I pray that your doctor is mistaken and that there is a more benign explanation for your situation. Try to keep busy in the rest of your life and don't let the uncertainty tear you down. You need to focus on positive things right now & not dwell on all the horrible thoughts that must be preying on your mind. Lean on your personal belief system as well as your BYC community. You will be in our thoughts and prayers in this difficult time.