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Most dangerous cutaneous malignancy, high metastatic potential, poor prognosis with metastatic spread.
Melanoma has been diagnosed in 73,870 people in the United States in 2015 and caused 9940 deaths.
Fair complexion, sun exposure, family history of melanoma, dysplastic nevus syndrome (autosomal dominant disorder with multiple nevi of distinctive appearance and cutaneous melanoma may be associated with 9p deletion), and presence of a giant congenital nevus (Table 67-1). Blacks have a low incidence.
|Total body nevi (higher number = higher risk)|
|Family or personal history|
|Light skin/hair/eye color|
|Poor tanning ability|
|UV exposure/sunburns/tanning booths|
Sun avoidance lowers risk. Sunscreens are not proven effective.
- Superficial spreading melanoma: Most common; begins with initial radial growth phase before invasion.
- Lentigo maligna melanoma: Very long radial growth phase before invasion, lentigo maligna (Hutchinson’s melanotic freckle) is precursor lesion, most common in elderly and in sun-exposed areas (esp. face).
- Acral lentiginous: Most common form in darkly pigmented pts; occurs on palms and soles, mucosal surfaces, in nail beds and mucocutaneous junctions; similar to lentigo maligna melanoma but with more aggressive biologic behavior.
- Nodular: Generally poor prognosis because of invasive growth from onset.
About half of melanomas carry an activating somatic mutation in the BRAF gene, often a valine to glutamate substitution at amino acid 600 (V600E). N-ras is mutated in about 20% and rare pts have activating mutations in c-kit. These mutations have been targeted by therapeutic agents that have antitumor activity.
Generally pigmented (rarely amelanotic); color of lesions varies, but red, white, and/or blue are common, in addition to brown and/or black. Suspicion should be raised by a pigmented skin lesion that is >6 mm in diameter, asymmetric, has an irregular surface or border, or has variation in color.
Best with thin lesions without evidence of metastatic spread; with increasing thickness or evidence of spread, prognosis worsens. Stages I and II (primary tumor without spread) have 85% 5-year survival. Stage III (palpable regional nodes with tumor) has a 50% 5-year survival when only one node is involved and 15–20% when four or more are involved. Stage IV (disseminated disease) has <5% 5-year survival.