Canker sores, which are a virus ( herpes simplex one when in the mouth) resolve on their own with or without treatment in 10-14 days. This is the first thing to mention to the doctor, as if he is paying attention, this is immediately going to remove HS1 as part of his differential diagnosis. If a biopsy is taken anywhere in an ulcerated lesion it is going to hit target cells, This is very different than a fine needle biopsy which may or may not hit malignant cells in a node for instance.