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MALIGNANT MELANOMA

Most dangerous cutaneous malignancy, high metastatic potential, poor prognosis with metastatic spread.

Incidence

Melanoma was diagnosed in 91,270 people in the United States in 2018 and caused 9320 deaths.

Predisposing Factors

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 68-1). Blacks have a low incidence.

TABLE 68-1Factors Associated with Increased Risk of Melanoma

Prevention

Sun avoidance lowers risk. Sunscreens are not proven effective.

Types

  1. Superficial spreading melanoma: Most common; begins with initial radial growth phase before invasion.

  2. 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).

  3. 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.

  4. Nodular: Generally poor prognosis because of invasive growth from onset.

Biology

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.

Clinical Appearance

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.

Prognosis

Best with thin lesions without evidence of metastatic spread; with increasing thickness, ulceration, or evidence of nodal spread, prognosis worsens. Stage I (primary tumor without spread) has 80−92% 15-year survival. Stage II (>1−4 mm) has a 51−62% 15−year survival. Stage III (regional nodes with tumor) has a 60% 15-year survival when 1−3 nodes are microscopically involved and 22–38% when 1−3 nodes are macroscopically involved or 4 or more are involved. Stage IV (disseminated disease) has <10% 15-year survival.

TREATMENT

TREATMENT Malignant Melanoma

Early recognition and local excision for localized disease is best; 1- to 2-cm margins are as effective as 4- ...

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