A 6-month-old female infant presented with a 3.0 × 2.2-cm nodular hyperpigmented left shoulder skin lesion. The results of a biopsy of the lesion were consistent with congenital melanocytic nevus. One year later, the lesion recurred at the resection site. The recurrent lesion was composed of multiple small brownish discolored areas, with the largest area measuring 1.0 cm in diameter at its greatest width, as well as a single 0.7-cm raised nodule. Examination of histologic sections showed epithelioid nevus cells arranged in clusters and diffuse sheets with moderate pleomorphism, mitosis, necrosis, and lack of cellular atypia with 3 to 4 mitosis per high-power field (Figures 1 and 2). Nine months after the shoulder re-excision, 2 enlarged left axillary lymph nodes ranging in size from 2.3 to 2.7 cm were excised. Examination of the excised lymph nodes revealed an architecture largely replaced by a diffuse proliferation of polyhedral cells with vesicular nuclei and small but conspicuous nucleoli. Once again mitotic figures (ranging from 1 to 6 per high-power field) and necrosis were identified (Figure 3). S100 stains were positive for tumor cells in the lymph nodes (inset of Figure 3).
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Pathologic Diagnosis: Malignant Melanoma
The incidence of congenital nevi in newborns is reported to be only 1% to 2%.1 The actual concern is the malignant potential of these nevi to convert into malignant melanoma. The large or giant melanocytic nevi (≥20 cm) are predominantly located over the posterior trunk and have a malignant transformation risk of 14%.1 The small (<2 cm) nevi that are found in 1% of newborn infants are less malignant, contributing to approximately 15% of malignant melanomas.2 However, melanoma remains an uncommon malignancy in children and adolescents, accounting for less than 3% of all pediatric malignancies, despite the dramatic increase in incidence of adult melanoma in recent years.2
Risk factors for malignant melanoma, such as giant cell congenital nevi, have been described. Other risk factors are xeroderma pigmentosum, a rare hereditary disorder characterized by defects in the repair of ultraviolet-induced DNA damage and dysplastic nevus syndrome. Conditions such as human immunodeficiency virus (HIV), leukemia, lymphoma, and renal transplantations have also been reported to be accompanied by an increased risk of melanoma.1
The prognosis of melanomas depends on the level and depth of invasion. Nodal metastases can develop in up to two thirds of children with Clark levels IV and V or a Breslow thickness of greater than 1.5 mm.3
There is much debate on the management of congenital melanocytic nevi. Some have suggested the prophylactic excision of all nevi, whereas others have argued against this approach because it provides insufficient evidence that failure to remove all nevi poses an increased risk of malignancy. Worrisome clinical findings include asymmetry of the lesion, irregular borders, variegated colors, and an increase in the diameter of the lesion.
Malignant melanoma may sometimes be confused with Spitz nevi. The original description by Spitz in 1948 includes lesions histologically similar to malignant melanoma, with a uniformly benign course in children. Spitz nevi constitute less than 1% of melanocytic nevi in children and appear as dome-shaped smooth red-tan lesions located mainly in the head, neck, and lower extremity.4 Microscopically, Spitz nevi share many features with melanomas. In childhood, the lesions appear to be more ominous because of the frequent finding of pagetoid growth and high mitotic rate in the superficial aspect of the lesion. Histologic attributes that strongly indicate melanoma as opposed to Spitz nevus are lack of maturation, mitosis in the deeper portion, marked nuclear pleomorphism and hyperchromasia, and an expansile architecture in the dermis. Since there is considerable overlap in the histologic features between Spitz nevi and malignant melanoma, with differentiation being generally difficult, some authors consider metastatic spread to be the only acceptable evidence of the malignant nature of the lesion.5
Our case was diagnosed as malignant melanoma arising from a congenital melanocytic nevus. The recurrent lesion, diagnosed as Spitz nevus, showed some of the overlapping features found in both Spitz nevus and malignant melanoma. Only when the lesion metastasized to the axillary lymph nodes was the diagnosis of malignant melanoma with a Clarke level IV and a Breslow thickness of 3.3 mm confirmed.