Atypical Mole Syndrome

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Disorder Subdivisions

  • None

General Discussion

Atypical mole syndrome, also called dysplastic nevus syndrome, is a disorder of the skin characterized by the presence of many mole-like tumors (nevi). Most people have 10-20 moles over their bodies. People with this syndrome often have more than 100 moles, at least some of which are unusual (atypical) in size and structure. These moles vary in size, location, and coloring. They are usually larger than normal moles (5mm or more in diameter) and have irregular borders. Changes in the appearance of these moles must be taken seriously by patients since such changes may foreshadow the onset of cancerous disease.

Individuals with atypical mole syndrome are at greater than others for developing cancer of the skin in the form of malignant melanoma. Atypical mole syndrome is thought by some clinicians to be a precursor or forerunner of malignant melanoma. This type of cancer may spread to adjacent parts of the skin or, through the blood and lymph circulation, to other organs.


Symptoms of atypical mole syndrome usually start during adulthood. The disorder is characterized by the presence of a greater than normal number of moles (often more than 100), unusually large moles (greater than 5 mm in diameter), and moles that are variable in color and may combine more than one color, including tan, brown, black, red and/or pink. These moles have irregular and fuzzy or indistinct borders.

The presence of dust-like melanin (pigments found in the skin), which gives the moles their color, and abnormally large nuclei of skin cells called melanocytes, all visible under the microscope, are characteristic of dysplastic nevus syndrome. The mole-like tumors may spread to adjacent parts of the skin, or through the blood and lymph circulation, to other organs. Certain changes in the melanocyte nuclei indicate when atypical mole syndrome may be changing to malignant melanoma.


Atypical mole syndrome is inherited, but the mode of inheritance is complex and not clearly understood. It is believed to be an autosomal dominant trait in some cases, and it may involve several genes on different chromosomes. Some cases also appear to occur sporadically as the result of random mutations.

Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child.

Affected Populations

Symptoms of atypical mole syndrome usually appear in adulthood. Males and females are affected in equal numbers.

In the United States, the prevalence of this syndrome has been reported as 2-5% of the white population, which is about half the rate reported for Australia and New Zealand. In Sweden, about 18% of white adults are thought to show clinical signs of dysplastic nevus syndrome, but only 8% had confirmed cellular (histological) characteristics of the disorder.

While it is clear that atypical mole syndrome can lead to malignant melanoma, it is not at all clear just what the exact risk is of any single atypical mole changing into a malignant form. The risk rises as the number of moles (nevi) rises. An atypical mole syndrome patient with a family history of malignant melanoma is at greater risk than is a patient without the family history.

The disorder is more common among persons of northern European background than among Afro-Americans or Asians.


Diagnosis of atypical mole syndrome is reasonably obvious if, on physical examination, an unusually large number of moles are found on the patient's arms, trunk and/or head. Parts of the body regularly exposed to sunlight are especially vulnerable. The patient's history will show that some of the moles will be peculiarly colored, or that the color has changed over time. Other moles will have grown in size and/or changed texture.

As soon as possible after one or more moles undergo changes, a biopsy is essential in order to determine if any of the cells that make up the mole have become cancerous.

Standard Therapies


Treatment is primarily a matter of preventive measures, such as staying out of the sun during the hottest time of the day, to lower the risk for malignant melanoma, and of regular self-examination and in-office examination so that any possible malignancies may be detected as early as possible and treated appropriately. It has been well documented that early detection and treatment of malignant melanoma improve the likelihood of successful treatment.

Affected individuals are advised to avoid direct sunlight and use a protective sunscreen. Other preventive measures include wearing a wide-brimmed hat, sunglasses, and protective clothing when in the sun, avoiding tanning machines, and protecting children (and especially infants) from excessive exposure to the sun.

It is not necessary, or even advised, to remove multiple atypical moles beforehand in an attempt to prevent development of malignant melanoma. However, any change in such a mole should be reported to one's physician immediately.

Investigational Therapies

Information on current clinical trials is posted on the Internet at All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222

TTY: (866) 411-1010


Further information on clinical trials, especially those sponsored by pharmaceutical companies, is available at:



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For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders, Inc.® (NORD). Cigna members can access the complete report by logging into For non-Cigna members, a copy of the complete report can be obtained for a small fee by visiting the NORD website. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational treatments (if available), and references from medical literature. For a full-text version of this topic, see