Atypical moles, also called dysplastic moles, are very common. An estimated one out of every 10 Americans has at least one atypical mole. These moles are larger than common moles, with borders that are irregular and poorly defined. Atypical moles also vary in color, ranging from tan to dark brown shades on a pink background. They have irregular borders that may include notches. They may fade into surrounding skin and include a flat portion level with the skin. These are some of the features that one sees when looking at a melanoma. When a pathologist looks at an atypical mole under the microscope, it has features that are in-between a normal mole and a melanoma.

For years, doctors have debated the risk of developing melanoma in people with atypical moles. Melanoma is a potentially deadly form of skin cancer that is diagnosed in about 40,000 Americans each year. It is now known that about half of the people with melanoma have numerous atypical moles on their bodies. The risk is greatest in people who also have extremely fair skin and heavy freckling, a sign of excessive sun exposure.

While atypical moles are considered to be pre-cancerous (more likely to turn into melanoma than regular moles), not everyone who has atypical moles gets melanoma. In fact, most moles -- both ordinary and atypical ones -- never become cancerous. Thus the removal of all atypical nevi is unnecessary. In fact, most of the melanomas found on people with atypical moles arise from normal skin and not an atypical mole.

Still, there is potentially great benefit in identifying persons at increased risk of melanoma. Individuals and family members with atypical moles from melanoma-prone families should be closely checked for melanomas. This has resulted in the diagnosis of a substantial number of curable melanomas.

People without a family history of atypical moles or melanoma have an increased risk of melanoma, but it is not as high as the risk observed in members of melanoma-prone families. Individuals with a single atypical mole on their bodies have a twofold risk of developing melanoma. The risk rises to 14-fold in those with 10 or more abnormal moles.

If there are a great many atypical moles and several family members have had melanoma, you need to be very careful. Still, it has not been shown that removing all the moles (sometimes in the hundreds) decreases the lifetime risk for melanoma. Melanoma usually arises de novo, i.e. not in a pre-existing benign mole. Also people with atypical moles should have annual eye exams, as ocular melanoma is also a big risk in these cases. One should be followed closely with a very low threshold to biopsy any lesion remotely suspicious. Getting detailed body photographs are an excellent way to follow moles to see if any are changing.

Although a physician bases the initial diagnosis of atypical moles on a physical examination, removing several moles and examining them under a microscope must confirm the diagnosis. This procedure, called a biopsy, is usually performed in your doctor's office using local anesthesia.

A pathologist will examine the tissue under a microscope and make the precise diagnosis. Diagnosis by biopsy is not exact, and in difficult cases doctors may split 50/50 down the middle as to whether a mole is melanoma or benign. If the pathologist uses the term "severely dysplastic" or "atypical melanocytic hyperplasia" or offers a long descriptive narrative it means he really is concerned about melanoma, but does not want to call it that.

Most dermatologists usually recommend that all patients with these severely dysplastic moles have them removed with a margin (0.5 cm-about a quarter inch) of clinically normal skin. Also many dermatologists recommend removing "moderate dysplasia" moles, if the biopsy didn't get all of it. Those with "mild dysplasia" can usually be left alone or watched.

Once the diagnosis of atypical moles is established, additional biopsies are performed only if melanoma is suspected, or if a new mole appears. Just as women who regularly examine their own breast are much more likely to be cured of breast cancer if it appears, self-exam of your skin once a month is the best defense against melanoma. Be sure to insist on a biopsy of any mole that is changing or growing.

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