Fine needle aspiration of malignant melanoma with myxoid features: A case report with molecular analysis

Malignant melanoma with myxoid features (MMM) is a rare melanoma variant in which tumor cells are embedded within a basophilic myxoid stroma. The stromal matrix is composed of acidic mucopolysaccharides, which are thought to be produced by mesenchymal stromal cells in response to melanoma invasion. Interestingly, this myxoid matrix is more often seen in metastasis from a primary tumor that does not have a myxoid stroma. The diagnosis of MMM on fine needle aspiration (FNA) can be confused with other myxoid tumors. Herein, we present a case of MMM diagnosed by FNA of a peri-auricular lymph node in an 89-year-old man with a history of resected malignant melanoma. We describe the clinical, cytohistological, and immunohistochemical findings, and present the unique molecular alterations that were identified. We also discuss the differential diagnosis and potential diagnostic pitfalls associated with MMM.