Any new, suspicious-looking spot on your skin, or a change in the shape, size or color of a mole, could be an early sign of skin cancer. Fortunately, the vast majority of skin blemishes are not cancerous, but you should have your doctor check any changes you notice anyway. To determine if an area of concern is cancerous, your doctor will first take your medical history and determine your risk factors, including any history of skin cancer in your family and the number of severe sunburns you've suffered. During your skin examination, the doctor will note the size, shape, color and texture of the suspicious area; check your lymph nodes for swelling and examine for any other potential signs of cancer. If the doctor feels it's needed, a skin biopsy will remove a small sample from the suspect area for further testing.
Read more about the diagnosis of skin cancer and melanoma.