Atypical Moles: A Risk Factor for Melanoma

More than 3 in 4 (approximately 76%)​ of skin cancers are diagnosed by primary care physicians. Atypical moles rarely progress to melanoma​. Only an estimated 1 in 33,000 atypical moles per year will progress to melanoma. Most cases of melanoma (> 70%) arise from de novo mutations. The presence of more than five atypical moles increases the risk of melanoma more than the presence of between 101 and 120 total moles (relative risk 6.89 vs 10.59), making the identification of atypical moles helpful for risk stratification and prevention of melanoma.

A recent American Family Physician (AFP) article reviewed atypical moles. These are usually found in sun-exposed areas in patients with fair skin; however, in patients with more pigmented skin, atypical moles are more common in non–sun-exposed regions such as the soles of the feet. Atypical moles are diagnosed clinically through visual inspection with or without dermoscopy. Visual inspection often consists of the ugly duckling assessment (ie, does this mole look different from the other moles this patient has?) and the ABCDE mnemonic (asymmetry, border irregularity, color unevenness, diameter ≥ 6mm, evolution). The ugly duckling assessment alone has a sensitivity of 85%-100%​, but may underdiagnose some patients with many uniformly atypical moles. Additional clinical decision rules for identifying melanoma may be found in this AFP article on melanoma. The use of dermoscopy in addition to visual examination significantly increases the sensitivity and specificity of diagnosis.

Familial atypical multiple mole melanoma syndrome is a clinical diagnosis made by the presence of more than 50 moles (in which many are atypical) and a first- or second-degree relative with melanoma. The condition is inherited in an autosomal dominant fashion. A referral for genetic testing for the CDKN2A gene variation may be considered.

Excisional biopsy of atypical moles with features concerning for melanoma is recommended with a margin of 1 to 3 mm and sufficient depth. Partial or scout biopsy is associated with tumor upstaging (increasing cancer stage after further evaluation) but may be considered in regions that are difficult for excisional biopsy.

Management of atypical moles after biopsy is guided by results. Lesions with mild or moderate atypia may be observed, even if margins are not clear. If repigmentation occurs, reexcision with 2 to 3 mm margins is recommended. Similarly, reexcision is recommended if clear margins have not been obtained in atypical moles with moderate-to-severe atypia. An algorithm can be found in Figure 9 of the recent AFP article on atypical moles. Atypical moles that have not been biopsied should be reevaluated every 3 to 12 months.

Prevention of melanoma is primarily through sun/UV protection. An AFP Community Blog post reviewed the risks and benefits of sun exposure, and an editorial in AFP discusses common concerns about health effects of sunscreen use. The US Preventive Services Task Force​ recommends minimizing exposure to UV radiation for persons aged 6 months to 24 years with fair skin types but finds insufficient evidence to recommend skin cancer screening. Indoor tanning​ is considered a carcinogen and increases the risk of melanoma.