Blue Nevus-Like Metastasis of a Cutaneous Melanoma Identified by Fluorescence In Situ Hybridization.

A blue nevus-like melanoma is a rare melanoma variant arising from or histologically similar to a blue nevus. It can be challenging to distinguish a cellular blue nevus from a blue nevus-like melanoma, particularly in cases of blue nevus-like melanoma lacking a transition from a clearly benign component. We present a case of a 78-year-old man who refused treatment for a previously existing melanoma and subsequently developed a gray nodule near the site of the previous melanoma. After fluorescence in situ hybridization revealed copy number gains in RREB1, this was diagnosed as a blue nevus-like metastatic melanoma. Blue nevus-like metastatic melanoma is most commonly seen near the site of the primary cutaneous melanoma. This entity should be considered in a patient with a history of melanoma and a new blue nevus-like lesion.