Atypical moles—also known as atypical nevi, dysplastic nevi, Clark nevi, and familial atypical nevi—were first described in 1978, when their association with malignant melanoma was recognized. These distinctive skin lesions were noted in 37 of 58 members in six families with histories of melanoma. (“The B-K mole syndrome,” Arch Dermatol. 1978;114(5):732-738)
While a single atypical mole does not increase one’s lifetime risk of malignant melanoma, these lesions are markers for melanoma, and they are sometimes difficult to distinguish from malignant lesions.
When multiple atypical moles are present, the risk for developing melanoma is increased—the greatest risk being in individuals who have more than 50 atypical moles and who have two or more family members with melanoma.
Atypical moles are considered by some to be precursors of malignant melanoma. However, most melanomas (80%) arise on normal skin, and most atypical moles do not progress to malignant melanoma. Thus, the presence of multiple atypical moles simply serves as a signal of increased risk; only those atypical moles that are worrisome for melanoma or that are changing need to be removed.
Features of Atypical Moles
- Age at onset: After six to 12 months of age; usually present by 20 years of age
- Location: Any site; can be in sun-protected areas. Back is usually most heavily involved
- Number: One to several hundred
- Size: No lower size limit; usually over 6 mm in diameter (the diameter of a pencil eraser)
- Color: Multiple shades of brown, dappled or variegated, dark pigmentation
- Shape: Round, oval, or asymmetric
- Border: Irregular or poorly demarcated; may have darker, raised center with lighter surrounding component (“fried-egg”)
- Surface: Usually raised and/or textured
Features of Normal Moles
- Age at onset: After six to 12 months of age; usually present by 20 years of age
- Location: Any site, but sun-protected areas usually have fewer
- Number: Few to several hundred
- Size: Mostly less than 6 mm in diameter
- Color: Typically uniform; no more than two shades of brown; usually lighter in pigmentation
- Shape: Round or oval
- Border: Smooth, regular; distinct edges
- Surface: Uniform; may be raised, but usually smooth
Features of Malignant Melanoma
- Age at onset: Usually adulthood, except in children with giant congenital moles or atypical mole syndrome
- Location: In men, mostly on trunk; in women, most often on lower extremities; can occur in any location, however, including mucous membranes
- Number: One, but may occur at more than one site over time
- Size: Can be any size
- Color: Variable, from light (as in amelanotic melanoma) to blue, brown, or black. Colors change over time. Usually multiple shades in one lesion
- Shape: Asymmetric and irregular, though nodular (round) melanomas occur
- Border: Usually irregular, with indistinct portions, except in some nodular melanomas
- Surface: Pebbled, raised, irregularly textured; occasionally smooth (nodular melanoma)
(Am Fam Physician. 2008;78(6):735-740, and National Cancer Institute Information Resources)
The incidence of malignant melanoma—the deadliest form of skin cancer—is increasing faster than any other malignancy. Individuals with multiple atypical moles are at higher risk. However, all people should limit their exposure to sunlight, which is clearly associated with melanoma. Anyone with an unusual-appearing mole, or one that is changing in any way, should seek professional medical evaluation.
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