Most malignant skin tumors develop on the visible outer layer of the skin (the epidermis), particularly on sun-exposed areas such as the face, head, hands, arms, and legs. In addition to sun exposure, family history may also play a role. The diagnosis of skin cancer usually requires a skin biopsy, in which a piece of skin is removed for examination under a microscope. If skin cancer is detected before it has spread to surrounding tissues, the chances of a complete cure are excellent.