No not all cancer is visible to the eye - my first biopsy came back inflamed tissue - the underside of my tongue on one side was red - the ENT said well its a large area of redness I don't know where to take from - if he had felt around he might have noticed that there was a lump in my tongue - there was no sore - so its very likely the tumor was under the surface - I thought it was merely scar tissue as I'd had a leukoplakia removed years before - I was wrong. So was he - he either didnt go deep enough or didn't take from the right area - two years later that's where the tumor was discovered. Now saying that - I agree with both of the previous opinions - likely not cancer - however go to a top ccc - have it checked out to ease your mind. Good luck. Dr.s aren't always right but a lot I hem do know what here talking about! Take care!