I Have Had A White Round Ulcer On My Gums

I have had a white round ulcer on my gums for two weeks. It only hurts when I eat or drink, then it aches. My dentist looked at it and said it presented as a classic canker sore. He wants to see me in a week. I am concerned it might be cancer because it hasn't healed. I had blood tests a week ago and by white count was 4.3 and my monocyte relative was 15.2