A definitive diagnosis of melanoma is made with an excisional biopsy that removes the mole and a margin of tissue surrounding it, or with a "punch" biopsy of the thickest part of the mole if it is large or in a difficult anatomical area to reach. These biopsies are outpatient procedures performed in your doctor's office. A pathologist will look at the sample under a microscope and determine if the cells are cancerous. The biopsy sample, along with other tests and procedures, allows the pathologist to determine the stage of disease, upon which treatment decisions are then made.
An excisional biopsy removes the mole and a margin of tissue surrounding it. Because melanomas can grow deep into the skin layer, your surgeon may remove tissue down to the subcutaneous layer — the lowermost portion — of skin. First, the area will be numbed with a local anesthetic. Your doctor will remove the mole and a margin of tissue and send this biopsy sample to a pathologist. The surgical area will be sewn closed. The procedure may take 30 minutes or less.
During a punch biopsy your doctor will take a core sample of the mole, preferably in its thickest part. Your doctor will numb the area first with a local anesthetic. The biopsy will be taken with a small tool that punches through the mole to an ascertained depth and removes the sample. The area is closed with stitches and the sample is sent to pathology for review.