Atypical moles

The skin cells that produce pigment (melanocytes) sometimes group together to form moles. Most people have at least 10 moles on their bodies.

Melanocytes can form abnormal moles, also called atypical moles or dysplastic nevi. These moles are not malignant themselves, but their presence is a warning of an inherited tendency to develop melanoma. Some people have only 1 or 2 atypical moles; some people may have more than 100. The tendency to develop atypical moles can run in families (inherited predisposition).

Early signs of melanoma in atypical moles

The American Cancer Society's ABCD rule of detection means watching for:¹

• Asymmetry . One half doesn't match the other half.
• Border irregularity . The edges are ragged, notched, or blurred.
• Color . The pigmentation is not uniform. Shades of tan, brown, and black are present. Dashes of red, white, and blue add to the mottled appearance. Changes in color distribution, especially the spread of color from the edge of a mole into the surrounding skin, also are an indicator of early melanoma.
• Diameter . The size of the mole is larger than 1/4 inch (6 mm), or about the size of a pencil eraser. Any growth of a mole should be of concern.

Atypical moles are seen most commonly on the back but may appear anywhere on the body, including below the waist, on the scalp, or on the breasts or buttocks. They may fade into surrounding skin and include a flat portion that is level with the skin surface. They may be smooth, slightly scaly, or have a rough, irregular, "pebbly" appearance.

Atypical moles usually are not present at birth but develop some time later.

Several types of atypical moles are known to develop before melanoma (melanoma precursors). Atypical moles are the most common precursor, but not all atypical moles develop into melanoma. Precursors to melanoma include:

• Giant congenital melanocytic nevus (giant hairy nevus or garment nevus).
• Small to medium-sized congenital melanocytic nevus.
• Some heavily pigmented lesions of the membrane that line the eyelids (conjunctiva).

Citations

1. American Cancer Society (2006). Cancer Facts and Figures 2006, pp. 1–56. Atlanta: American Cancer Society. Available online: http://www.cancer.org/docroot/STT/stt_0.asp.