A melanocytic nevus (also known as nevocytic nevus, nevus-cell nevus, and commonly as a mole) is a usually noncancerous condition of pigment-producing skin cells. It is a type of melanocytic tumor that contains nevus cells. A mole can be either subdermal (under the skin) or a pigmented growth on the skin, formed mostly of a type of cell known as a melanocyte. The high concentration of the body's pigmenting agent, melanin, is responsible for their dark color. Moles are a member of the family of skin lesions known as nevi (singular "nevus"), occurring commonly in humans. Some sources equate the term "mole" with "melanocytic nevus", but there are also sources that equate the term "mole" with any nevus form. The majority of moles appear during the first two decades of a person's life, with about 1 in every 100 babies being born with moles. Acquired moles are a form of benign neoplasm, while congenital moles, or congenital nevi, are considered a minor malformation or hamartoma and may be at a higher risk for melanoma.
Signs and symptoms
According to the American Academy of Dermatology, the most common types of moles are skin tags, raised moles, and flat moles. Benign moles are usually brown, tan, pink, or black (the latter especially on dark-colored skin). They are circular or oval and are usually small (commonly 1–3 mm), though some can be larger than the size of a typical pencil eraser (>5 mm). Some moles produce dark, coarse hair. Common mole hair removal procedures include plucking, cosmetic waxing, electrolysis, threading, and cauterization.
Aging Moles tend to appear during early childhood and during the first 30 years of life. They may change slowly, becoming raised, changing color, or gradually fading. Most people have between 30 and 40 moles, but some have as many as 600. The number of moles a person has was found to have a correlation with telomere length. However, the relation between telomeres and aging remains uncertain.
Complications The American Academy of Dermatology says that the vast majority of moles are benign. Data on the chances of transformation from melanocytic nevus to melanoma are controversial, but it appears that about 10% of melanomas have a precursor lesion, of which about 10% are melanocytic nevi. Therefore, it appears that melanoma quite seldom (1% of cases) has a melanocytic nevus as a precursor.
Cause The cause of this condition is not clearly understood, but it is thought to result from a defect in embryologic development during the first 12 weeks of pregnancy. The defect is thought to cause a proliferation of melanocytes, the cells responsible for normal skin color. When melanocytes are produced at an extremely rapid rate, they form in clusters instead of spreading out evenly, resulting in abnormal skin pigmentation in some areas of the body.
Genetics Genes can influence a person's moles. Dysplastic nevus syndrome is a largely hereditary condition that causes a person to have a large quantity of moles (often 100 or more), with some larger than normal or atypical. This often leads to a higher risk of melanoma, a serious type of skin cancer. Dysplastic nevi are more likely than ordinary moles to become cancerous. While dysplastic nevi are common, and many people have a few of these abnormal moles, having more than 50 ordinary moles also increases the risk of developing melanoma. In the general population, a slight majority of melanomas do not form in existing moles but rather create new growths on the skin. Somewhat surprisingly, this pattern also applies to those with dysplastic nevi. These individuals are at a higher risk of melanoma occurring not only where there is an existing mole but also in areas without moles. Consequently, such persons need regular examinations to check for changes in their moles and to identify any new ones.
Sunlight Ultraviolet (UV) light from the sun causes premature ageing of the skin and skin damage that can lead to melanoma. Researchers hypothesized that overexposure to UV, including excessive sunlight, may play a role in the formation of acquired moles. However, more research is needed to determine the complex interaction between genetic makeup and overall UV exposure. Some strong indications supporting this hypothesis (but falling short of proof) include:
The relative lack of moles on the buttocks of people with dysplastic nevi The known influence of sunlight on freckles (spots of melanin on the skin, distinct from moles) Studies have found that sunburns and excessive sun exposure can increase risk factors for melanoma. This is in addition to the higher risk already faced by individuals with dysplastic nevi (the uncertainty is regarding acquiring benign moles). To prevent and reduce the risk of melanoma caused by UV radiation, the American Academy of Dermatology and the National Cancer Institute recommend:
Staying out of the sun between 10 a.m. and 4 p.m. standard time (or whenever one's shadow is shorter than one's height) Wearing long sleeves and trousers Wearing hats with a wide brim Applying sunscreens Wearing sunglasses that have UV-deflecting lenses
Diagnosis
Clinical diagnosis can be made with the naked eye using the ABCD guideline or by using dermatoscopy. An online-screening test is also available to help screen out benign moles.
Classification Melanocytic nevi can mainly be classified by depth, being congenital versus acquired, and/or specific dermatoscopic or histopathologic patterns:
Depth
Congenital versus acquired Congenital nevus: Small to large nevus present at or near time of birth. Small ones have low potential for forming melanomas, however the risk increases with size, as in the giant pigmented nevus. Acquired nevus: Any melanocytic nevus that is not a congenital nevus or not present at birth or near birth.
Specific dermatoscopic or histopathologic patterns
Recurrence Recurrent nevus: Any incompletely removed nevus with residual melanocytes left in the surgical wound. It creates a dilemma for the patient and physician, as these scars cannot be distinguished from a melanoma.
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