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A 62-year-old healthy female office manager with fair skin visited her dermatologist for the evaluation of a recently appearing itchy black mole on her left thigh. Upon examination, the mole was approximately 8 mm in diameter with an asymmetrical shape, irregular borders, black and brown coloration, and a flat surface. An excisional biopsy with 1-cm surgical margins was performed revealing a superficial spreading melanoma of 0.6-mm thickness without ulceration or evidence of rapid cell division. There was no disease spread beyond the primary anatomic site, and the patient was followed with regular examinations, which revealed no recurrence or spread during the following 5 years.


Melanoma is a malignancy of pigment-producing cells (melanocytes) principally found in the skin. It is the fifth most common form of cancer in the United States, with more than 75,000 cases diagnosed each year. Although fewer than 5% of skin cancers are melanomas, four out of five deaths from skin cancer are related to melanoma.

Melanomas typically present, as in the patient described, as nonuniform pigmented skin lesions that have changed over time. The lesions may have shades of brown, black, red, or blue discoloration. The appearance usually is asymmetrical, and the boundaries are often indistinct or irregular. At diagnosis, the size usually exceeds a half centimeter.

Melanoma occurs much more frequently among whites than among those of other races. It tends to arise more frequently in older persons but can occur as early as the second or third decades of life. Fair-skinned persons, as in the patient described earlier, are at increased risk as are those with light hair color, blue eyes, and a predisposition to freckling.

Persons with a family history of melanoma are at increased risk, and a number of genes have been associated with a predisposition to developing this disease. Persons who have had a previous melanoma are at greatly elevated risk of developing a second melanoma. By far, the strongest environmental risk factor for this disease is exposure to ultraviolet (UV) radiation. This can occur through sunlight exposure, as demonstrated by cumulative indices of exposure, as well as frequency of sunburn events. The use of tanning beds also has been linked to melanoma risk, especially among young adults who are regular users.

A diagnosis of melanoma is confirmed by a surgical biopsy that removes some or all of the lesion for microscopic examination by a pathologist. There are five subtypes of melanoma, with about two thirds classified as the superficial spreading type. These cancers begin as a proliferation of melanocytes in the basal layer of the skin and tend to grow by radial (outward) expansion followed eventually by vertical (upward) expansion.

Several microscopic features have been shown to be related to the prognosis of melanomas. One of the most important attributes is the vertical penetration of the lesion, with ...

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