A cancerous mole typically has certain physical characteristics that make it distinguishable from a non-cancerous, or benign, mole. The initialism ABCD can help you remember the characteristics of a cancerous mole. "A" stands for asymmetrical, because cancerous moles generally aren't the same shape, size or thickness on both sides; "B" stands for borders, because cancerous moles usually have jagged, badly delineated borders. "C" stands for color, because these moles are usually irregularly colored, mottled or dappled; "D" stands for diameter, because cancerous moles are usually larger than 6 mm (0.24 inches) in size.
Just because a mole fits some or all of these visual criteria, it doesn't necessarily mean it's a cancerous mole. Usually only a dermatologist can make that distinction. A doctor may choose to remove the mole immediately in either case.
Not all moles or skin tumors are cancerous. Most are probably benign. Skin moles known as dysplastic nevi may possess some of the characteristics of a cancerous mole, and other skin growths may also develop suspicious characteristics. Sometimes, these moles can become cancerous later on. People who have them may be considered to have a higher risk for skin cancer, particularly malignant melanoma.
Benign moles are usually fairly uniform in appearance. They are generally symmetrical in shape, with clearly defined, smooth edges. They are often the same color as the skin, and if they are a different color, then that color will show little variation across the surface of the mole. Benign moles are typically no more than 6 mm (0.24) in diameter. Size alone does not always indicate a cancerous mole, but, if a mole shows other characteristics of malignancy, and is larger than 6 mm (0.24 inches) in size, it could be a cause for concern.
Moles that are large, uneven in shape, or jagged around the edges could be cancerous. Moles that are not uniform in color could be cancerous. Moles that change in shape, color, or size could be cancerous.
It is considered important to have all moles, skin growths, and tumors evaluated by a dermatologist. Many moles with characteristics of malignancy are not, in fact, cancerous. Many dermatologists practice immediate removal of all moles with cancerous characteristics, as a preventative measure. Some forms of skin cancer, such as melanoma, can spread quickly and metastasize to other parts of the body. Most dermatologists advocate monitoring the appearance of all moles and seeking medical attention if a cancerous mole is suspected.