Melanoma developing in a nevoid melanocytoma with myxoid changes: a case report

Nevoid and myxoid melanoma are rare variants of melanoma; association of the two is a unique finding. Nevoid melanoma is characterized by morphologic resemblance to a nevus, whereas myxoid melanoma demonstrates a basophilic mucinous matrix. We present an atypical case of a melanoma progressing from a nevoid melanocytoma with myxoid changes. A 78-year-old female presented with a pigmented growth on her right thigh. Biopsy demonstrated a biphenotypic melanocytic proliferation composed of a nodule showing epithelioid melanocytes with enlarged nuclei, prominent nucleoli, lack of maturation, and abundant amphophilic cytoplasm with a rare mitotic figure. These findings were suggestive of melanoma along with a nevoid dermal component and myxoid stroma. FISH testing revealed a homozygous loss of 9p21 in the atypical component. SNP-microarray from the nevoid component demonstrated three abnormalities including a gain of whole chromosome 8, as well as loss of a copy of nearly an entire chromosome 9 and 16q most consistent with a melanocytoma.