CASE #1: Amelanotic melanoma

Melanoma is a malignant tumor of melanocytes in the skin and represents a substantial public health problem. Nearly one-fifth of patients develop metastatic disease, which is associated with extremely high mortality.1 The overall incidence and mortality rates have also been rising in recent decades.2 Melanoma usually presents as an asymptomatic brown or black macule with irregular borders and variegated colors.

Amelanotic melanoma (AM) is a unique presentation of melanoma. While the term amelanotic technically refers to lesions lacking pigment, amelanotic melanoma has been used to describe melanomas with minimal pigment or with pigmentation adjacent to the lesions.3 AM is a tumor many dermatologists are wary of because the lesions lack the usual clues to melanoma but behave in an equally aggressive manner. Lesions often present as nonspecific pink, scaly plaques or pink papules/nodules, lacking the classic pigment and color variegation seen with typical melanomas. While any subtype of melanoma may lack pigment, subungal melanomas are more common, with 25% being amelanotic.4

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The incidence of AM has been reported to range from 1.8 to 8.1% of melanomas.5 The differential diagnosis of AM is extensive, including both benign and malignant tumors. These tumors can be confused with a variety of other skin lesions, including such benign neoplasms as seborrheic keratoses, nevi, actinic keratoses, and verruca. AMs are often biopsied because of clinical suspicion of basal cell carcinoma.1

AMs are commonly misdiagnosed and incorrectly treated before definitive histologic analysis.5 Most studies, however, do not show a worse prognosis with AMs compared with pigmented melanomas; however, comparative prognostic studies controlling for tumor thickness are lacking.6

Melanoma is thought to arise through a stepwise pathway of tumor progression in which both genetics and sun exposure play important roles. The gene locus CDKN2A encodes proteins that are important in regulating cell-cycle progression. This gene has been associated with familial melanoma and has also recently been observed in patients with AM.7

The treatment for AM is similar to that for pigmented melanomas, with wide local excision being the standard of care. The margins of excision are generally determined by the thickness of the melanoma.

Due to the size of the lesion, this patient underwent wide local excision of his amelanotic melanoma by general surgery. The patient also underwent sentinel lymph node biopsy, which was negative.