One half of a mole or skin spot doesn't match the other half. Blue and white may appear. Any mole or spot that grows to more than one-fourth inch, about the size of the end of a pencil eraser. Malignant melanoma is one of three common forms of skin cancer, but not the most common. That distinction belongs to basal cell carcinoma, with about one half million cases reported annually.
Basal cells make up the base of the epidermis, the outermost covering of the body.
UV radiation can cause these cells to reproduce too fast, producing a tumorous growth. They often bleed, crust over, and open to bleed again. The cancer may be an itchy or tender reddish patch that comes and goes. Sometimes it's a pale splotch, like a scar, and sometimes a circular growth with a raised border and depressed center. Squamous cell carcinoma, the second most common skin cancer, accounts for about 100,000 cases each year.