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Precursors of Cutaneous Melanoma

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Precursors of melanoma are lesions that are benign per se but have the potential of turning malignant and thus giving rise to melanoma. Two such entities are recognized: (1) dysplastic melanocytic nevi (NMN) and (2) congenital NMN.

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Dysplastic Melanocytic Nevus

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ICD-9: 238.2 ○ ICD-10: D48–5 Image not available.

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  • Dysplastic nevi (DN) are a special type of acquired, circumscribed, pigmented lesions that represent disordered proliferations of variably atypical melanocytes.

  • DN arise de novo or as part of a compound melanocytic nevus.

  • DN are clinically distinctive from common acquired nevi: larger and more variegated in color, asymmetric in outline, irregular borders; they also have characteristic histologic features.

  • DN are regarded as potential precursors of superficial spreading melanoma (SSM) and also as markers of persons at risk for developing primary malignant melanoma of the skin, either within the DN or on normal skin.

  • DN occur either sporadically or in the context of the familial DN syndrome: kindreds with familial multiple DN and melanomas (formerly FAMMM, or B-K mole syndrome).

  • Synonym: atypical melanocytic nevus.

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Epidemiology

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Age of Onset
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Children and adults.

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Prevalence
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DN are present in 5% of the general white population. They occur in almost every patient with familial cutaneous melanoma and in 30–50% of patients with sporadic nonfamilial primary melanomas of the skin.

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Sex
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Equal in males and females.

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Race
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White persons. Data on persons with brown or black skin are not available; DN are rarely seen in the Japanese population.

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Transmission
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Autosomal dominant.

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Pathogenesis

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Multiple loci have been implicated in familial melanoma/DN syndrome, and it is likely that DN is a complex heterogeneous trait. It is assumed that an abnormal clone of melanocytes can be activated by exposure to sunlight. Immunosuppressed patients (renal transplantation) with DN have a higher incidence of melanoma. DN favor the exposed areas of the skin, particularly intermittently sun exposed (e.g., back) and this may be related to the degree of sun exposure; however, DN may also occur in completely covered areas.

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Clinical Manifestation

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Duration of Lesions
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DN usually arise later in childhood than common acquired NMN, which first appear in late childhood, just before puberty. New lesions continue to develop over many years in affected persons; in contrast, common acquired NMN do not appear after middle age and disappear entirely in older persons. DN are thought not to undergo spontaneous regression at all or at least much less than common acquired NMN. Also, whereas common NMN are usually in a roughly comparable stage of development in a given body region (e.g., junctional, compound, dermal), DN appear “out of ...

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