These names refer to the types of skin cells from which these cancers are derived.
Basal cells occur in smaller numbers and are located in the lowest part of the epidermis.
Of the two, basal-cell carcinoma usually grows more slowly. Basal carcinoma very rarely spreads through the blood or lymph to distant parts of the body, and is considered a cancer mostly because it invades and destroys the tissues around it. Malignant melanoma, on the other hand, may be life threatening if not treated early. Melanoma commonly, but not always, appears as a brownish-black spot or bump in the skin that enlarges and sometimes bleeds. Sometimes melanomas arise in moles that have been present for many years.