To diagnose skin cancer, a doctor reviews all symptoms, and checks the skin for any unusual growths or abnormal patches of skin. If skin cancer is suspected, a biopsy is performed on the growth or area of skin in question. Once the results of the biopsy are reviewed, the type of cancer can be determined, and a treatment plan created. Those who experience any skin changes, or have changes to existing moles or birthmarks, should see a doctor as soon as possible; early detection is key in successfully treating skin cancer.