Metastatic melanoma to the skin simulating blue nevus

Cutaneous metastases from melanoma can mimic primary melanoma and melanocytic nevi. Recognition of a metastatic lesion is of great importance for proper staging and treatment decisions. In this study, a potential diagnostic pitfall is described and discussed: dermal metastases from cutaneous melanoma simulating blue nevus, a phenomenon that has received little attention. Ten blue nevus-like lesions from three patients are presented. All contained pigmented melanocytes and melanophages in variable proportions arranged in a blue nevus-like growth pattern. The blue nevus-like metastases occurred in the same anatomic region as the primary tumor or, as in one patient, near the skin scar of a dissected lymph node metastasis. Histologic clues of metastatic melanoma included the presence of atypical epithelioid melanocytes, mitotic figures, and an associated inflammatory cell infiltrate at the periphery of the lesion. Although such histologic features facilitate the recognition of a metastasis, clinical correlation is essential for a definitive diagnosis.