(Dysplastic Nevus; Atypical Nevus)
Atypical moles are nevi with a slightly different clinical and histologic appearance (disordered architecture and atypia of melanocytes). Most melanomas arise de novo. Risk factors for melanoma include increased number of atypical moles and increased exposure to ultraviolet radiation and sun. Some patients have only one or a few atypical moles; others have many.
The propensity to develop atypical moles may be inherited (autosomal dominant) or sporadic without apparent familial association. Familial atypical mole–melanoma syndrome refers to the presence of multiple atypical moles and melanoma in ≥ 2 1st-degree relatives. These patients are at markedly increased risk (25 times) of melanoma.
Atypical moles are often larger than other nevi (> 6 mm diameter) and primarily round (unlike many melanomas) but with indistinct borders and mild asymmetry. In contrast, melanomas have greater irregularity of color and may have areas that are red, blue, whitish, or depigmented with a scarred appearance.
Atypical moles must be differentiated from melanoma. Features that suggest melanoma, known as the ABCDEs of melanoma, are
A: Asymmetry—asymmetric appearance
B: Borders—irregular borders (ie, not round or oval)
C: Color—color variation within the mole, unusual colors, or a color significantly different or darker than the patient's other moles
D: Diameter—>6 mm
E: Evolution—a new mole in a patient >30 years of age or a changing mole
Although clinical findings can sometimes establish a diagnosis of atypical moles (see table Characteristics of Atypical vs Typical Moles ), visual differentiation between atypical nevi and melanoma can be difficult; biopsy of the worst-appearing lesions should be done to establish the diagnosis and to determine the degree of atypia. Biopsy should aim to include the complete depth and breadth of the lesion; excisional biopsy is often ideal.
Characteristics of Atypical vs Typical Moles
Patients with multiple atypical moles and a personal or family history of melanoma should be examined regularly (eg, yearly for family history of melanoma, more often for personal history of melanoma). Some dermatologists do imaging of the skin using a hand-held instrument (dermoscopy) to see structures not visible to the naked eye. Dermoscopy can reveal certain high-risk characteristics suggestive of melanoma (eg, blue-white veil, irregular dots and globules, atypical pigment network, reverse network).
Prophylactic removal of all atypical moles is not effective in preventing melanoma and is not recommended. However, atypical moles may warrant removal for any of the following conditions:
Patients with atypical moles should avoid excessive sun exposure and use sun protection. Patients who are vigilant about sun protection should be counseled to take sufficient supplemental vitamin D. Also, they should be taught self-examination to detect changes in existing moles and to recognize features of melanomas. Full-body photography may help detect new nevi and monitor existing nevi for changes. Regular follow-up examinations are recommended.
If patients have a history of melanoma (whether developing from atypical moles or de novo) or other skin cancers, 1st-degree relatives should be examined. Patients who are from melanoma-prone families (ie, ≥ 2 1st-degree relatives with cutaneous melanomas) have a high lifetime risk of developing melanomas. The entire skin (including the scalp) of members of an at-risk family should be examined at least once to determine risk and needed follow-up.
Risk of melanoma is higher if patients have increased numbers of atypical moles, increased sun exposure, or familial atypical mole–melanoma syndrome.
Because clinical differentiation from melanoma can be difficult, biopsy the most suspect atypical moles.
Closely follow patients with atypical moles, particularly those at higher risk of melanoma, and do full-body photography.
Recommend sun protection (with supplemental vitamin D) and self-examination for high-risk changes.
Do full-body examinations of all 1st-degree relatives of patients who have melanoma.