Atypical nevi, also called atypical moles or dysplastic nevi, have been associated with an increased risk of developing melanoma. However, the possibility of an atypical mole transforming into skin cancer, and the appropriate precautions to take when an individual has one or more atypical moles, have long been debated in the dermatological community.
What are atypical nevi?
Atypical nevi are abnormal moles on the body. These moles exist in a continuum-like scale in between normal moles and melanoma. They are generally larger than normal moles, and may come in a variety of colors such as tan, varying shades of brown, red, black, or blue. Atypical nevi are often evaluated using the same ABCDE characteristics as melanoma, which includes evaluating possible asymmetry, abnormal borders, colors, diameters, and any evolutions or changes over time. Atypical nevi may be larger than 6 mm in length, or roughly the size of a pencil eraser, and may have pebble-looking elevations within them.1-3
In many cases, a biopsy of an atypical nevi may be performed to determine if it is truly an atypical nevus or if it is a potential melanoma. In the case of an atypical mole that is not melanoma, the biopsy results may indicate its severity. These severities include categories such as mildly dysplastic, moderately dysplastic, and severely dysplastic, among other potential classifications.4-5 It has been estimated that roughly one in ten individuals will have at least one atypical nevus, and those who are fair skinned or who are of northern European heritage have the highest chance of having at least one atypical nevus.6
Atypical nevi and melanoma risk
Although atypical nevi are considered to be in between regular moles and melanoma, and approximately 20% of melanomas come from a dysplastic nevus, the risk of any singular existing atypical nevi transforming into melanoma is very rare. One study found that the risk of an atypical mole turning into melanoma over an individual’s lifetime is less than 0.1% for both men and women.6 More research needs to be performed to determine the exact rate of transformation of dysplastic nevi to melanoma, however, these results indicate that the chance of any one atypical mole transforming is incredibly rare. The vast majority of melanomas will arise on a completely new area of skin that is not already inhabited by an atypical mole.2,6
This low risk has even led several experts to suggest that atypical moles that are mild-to-moderately dysplastic should not be completely removed after being biopsied. Only atypical moles that are considered moderate-to-severely dysplastic should be considered for removal in order to decrease an individual’s risk of developing melanoma.4,5 However, further study needs to be completed to determine the most appropriate course of action with an atypical mole, and each decision should be made on a case-by-case basis by an individual’s dermatologist.
Despite the low risk of direct transformation from dysplastic nevi to melanoma, individuals with one or more atypical nevi have been found to be at an increased risk of developing skin cancer in general. It has been estimated that individuals with ten or more atypical moles may be at a 12-times higher risk of developing melanoma than those with fewer or no atypical moles. This risk also increases for individuals with atypical mole syndrome (those with more than 100 moles, at least one atypical mole, and at least one mole larger than 8 mm in diameter), individuals who have a family history of melanoma, and those who have a history of familial atypical multiple mole melanoma syndrome (FAMMM), which is a combination of both family history of melanoma and atypical mole syndrome.2,6,7
How to Spot an Atypical Mole. Skin Cancer Foundation. https://www.skincancer.org/skin-cancer-information/atypical-moles/warning-signs-and-images. Accessed July 20, 2018.
Atypical Moles. American Osteopathic College of Dermatology. https://www.aocd.org/page/AtypicalMoles. Accessed July 20, 2018.
Common Moles, Dysplastic Nevi, and Risk of Melanoma. National Institutes of Health. National Cancer Institute. https://www.cancer.gov/types/skin/moles-fact-sheet. Published April 27, 2018. Accessed July 20, 2018.
Bath C. Low Risk of Transformation to Melanoma for Biopsy-Diagnosed Mildly or Moderately Dysplastic Nevi. The ASCO Post. http://www.ascopost.com/issues/september-15-2013/low-risk-of-transformation-to-melanoma-for-biopsy-diagnosed-mildly-or-moderately-dysplastic-nevi/. Published September 15, 2013. Accessed July 20, 2018.
KK Reddy, Farber MJ, et al. Atypical (dysplastic) nevi: Outcomes of surgical excision and association with melanoma. JAMA Dermatol. Aug 2013; 149(8), 928-34.
Goldstein AM, Tucker MA. Dysplastic Nevi and Melanoma. Cancer Epidemiol Biomarkers Prev. Apr 2013; 22(4), 528-32. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3616416/. Accessed July 20, 2018.
Atypical Moles (Dysplastic Nevi). Skin Cancer Foundation. https://www.skincancer.org/skin-cancer-information/atypical-moles. Accessed July 20, 2018.