Diagnosis of blue nevus-like metastatic uveal melanoma confirmed by fluorescence in situ hybridization (FISH) for monosomy 3.

Metastatic melanoma can on rare occasion simulate the appearance of a blue nevus clinically and/or histopathologically, which may lead to diagnostic confusion and delay in treatment. Given the known difficulty in recognizing a small dermal blue nevus-like melanoma metastasis by light microscopic findings alone, recent discoveries of unique cytogenetic aberrations in various types of melanomas have led pathologists to explore cytogenetic techniques as an ancillary diagnostic tool. Herein, we report a case of a 58-year-old man with a history of uveal melanoma, in which fluorescence in situ hybridization (FISH) analysis for monosomy 3 helped confirm a diagnosis of blue nevus-like uveal melanoma metastasis. The patient had presented clinically with a new small 1-mm dark blue-gray macule on the forehead. Histopathologically, a small dermal nodule of pigmented epithelioid melanocytes and melanophages was found with a rare mitotic figure. The pathologist's suspicion of a blue nevus-like melanoma metastasis was confirmed by FISH analysis: both the tumor cells of the patient's prior uveal melanoma and the melanocytes of the new dermal blue nevus-like nodule carried only one copy of chromosome 3. Furthermore, deletion of 1p36 and amplifications of 8q32 were also identified.