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Updated March 06, 2009

Definition: A nevus is a benign (non-cancerous) melanocytic tumor, more commonly called a mole. Nevi (the plural of nevus) are not usually present at birth but begin to appear in children and teenagers. Most moles will never cause any problems, but a person who has 50 or more moles is more likely to develop melanoma, the most aggressive form of skin cancer.

There are multiple types of nevi. A dysplastic (or "atypical") nevus is a large, irregularly-shaped type that particularly increases a person's risk of melanoma: About 50% of melanoma cases occur in people who have dysplastic nevi. People with this condition should have a thorough skin exam by a dermatologist every six months. Moles usually appear late in childhood, but some are present at birth in those with a condition called "congenital melanocytic nevi." The lifetime risk of getting melanoma for people with congenital melanocytic nevi has been estimated to be up to 10%, depending on the size of the nevus.

Also Known As: mole, melanocytic tumor
Common Misspellings: nevis
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