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Pigmented lesions are among the most common findings on skin examination. The challenge is to distinguish cutaneous melanomas, which account for the overwhelming majority of deaths resulting from skin cancer, from the remainder, which with rare exceptions are benign. Cutaneous melanoma can occur in adults of all ages, even young individuals, and people of all colors; it is located on the skin, where it is visible; and it has distinct clinical features that make it detectable at a time when complete surgical excision is possible. Examples of malignant and benign pigmented lesions are shown in Fig. 33-1.
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Melanoma is an aggressive malignancy of melanocytes: pigment-producing cells that originate from the neural crest and migrate to the skin, meninges, mucous membranes, upper esophagus, and eyes. Melanocytes in each of these locations have the potential for malignant transformation. In the United States, nearly 69,000 individuals were expected to develop melanoma and approximately 9000 were expected to die in 2010. Although the overall incidence and mortality have increased over the past decades, the mortality rates for younger patients have flattened, but those rates for individuals older than age 65 years have continued to increase. It is predominantly a malignancy of white-skinned people (98% of cases), and the incidence correlates with latitude of residence, providing strong evidence for the role of sun exposure. Men are affected slightly more than women (1.3:1), and the median age at diagnosis is the late fifties. Dark-skinned populations (such as those of India and Puerto Rico), blacks, and East Asians also develop melanoma, albeit at rates 10–20 times lower than those in whites. Cutaneous melanomas in these populations are diagnosed more often at a higher stage, and patients tend to have worse outcomes. Furthermore, in nonwhite populations, there is a much higher frequency of acral (subungual, plantar, palmar) and mucosal melanomas.
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The strongest risk factors for melanoma are the presence of multiple benign or atypical nevi and a family or personal history of melanoma (Table 33-1). The presence of melanocytic nevi, common or dysplastic, is a marker for an increased risk of melanoma. Nevi have been referred to as precursor lesions because ...