Melanocytic nevi are noncancerous growths made up of melanocytes that produce melanin. They can be present at birth or appear later in life and tend to occur more in certain families, people with light skin, and those who spend more time in the sun. They have the potential to become malignant, so prevention includes protecting the skin from the sun and watching existing moles closely for suspicious changes. Treatment includes removing the mole if it looks unsightly or shows signs of possible melanoma.
A melanocytic nevus, or mole, is a benign or noncancerous growth made up of cells known as melanocytes. Melanocytes produce a pigment called melanin, which gives skin its color, and when these cells clump together, a mole forms. A melanocytic nevus can be present at birth or appear later in life. Melanocytic nevi tend to occur to a greater extent in certain families, in people with light skin and in those who have spent more time in the sun. Occasionally, a melanocytic nevus can undergo changes that lead to the formation of a cancerous growth called a melanoma.
Melanocytic nevi occur not only in humans but in all mammals. Those that are present at birth are known as congenital melanocytic nevi and can be larger than moles acquired later in life, with giant versions measuring over 1.2 inches (about 3 cm). Melanocytes do not normally cluster together, so while they are common, melanocytic nevi are technically abnormal collections of pigment cells. Melanocytic nevi are acquired gradually throughout life, reaching a peak in middle age, then slowly declining in old age. The decrease in the formation of new moles after middle age is combined with a greater tendency for existing moles to disappear, so that older people generally tend to have fewer moles.
Although melanocytic nevi are examples of what are called benign neoplasms or noncancerous growths, they have the potential to become malignant or cancerous. A congenital melanocytic nevus carries an increased risk of developing melanoma. Prevention can be done by protecting the skin from the sun and watching existing moles closely for signs of suspicious changes such as itching, bleeding, or changes in shape, color, or size.
Any mole containing suspicious nevus cells can be removed and examined under a microscope to check for cancer. For people who have a large number of melanocytic nevi, a topographic map or snow map can be created. This map represents the whole body and records the location and characteristics of each melanocytic nevus.
A melanocytic nevus is usually not treated, but plastic surgery may be used to remove it if it looks unsightly, sticks to clothing causing irritation, or shows suspicious signs that indicate possible melanoma. Where a mole is known not to be cancerous, it is sometimes possible to shave it. Larger moles, or those that may be malignant, are usually completely removed by cutting, and the wound is then closed. Once removed, a melanocytic nevus can be passed on to a pathology department, where it can be examined to determine if cancer is present.
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