Tsao et al1 recently proposed a model to estimate the risk of malignant transformation of melanocytic nevi (MN) into cutaneous melanoma (CM) based on the rate of nevus-associated CM and on MN counts in the white US population stratified by 10-year age groups. The annual transformation rates of a single MN into CM ranged from a minimum of less than 1 in 200 000 in patients younger than 40 years to a maximum of 1 in 33 000 for men older than 60 years. This can be explained by higher MN counts and lower CM incidence in young persons and lower MN counts and higher CM incidence in older persons. For a 20-year-old individual, the lifetime risk for an MN transforming into CM was estimated to be 1 in 3164 for men and 1 in 10 800 for women. They conclude that the risk for a particular mole to become melanoma is low and that prophylactic excision of benign-appearing MN would be of limited benefit.
Bauer J, Garbe C. Risk Estimation for Malignant Transformation of Melanocytic Nevi. Arch Dermatol. 2004;140(1):127. doi:10.1001/archderm.140.1.127-a