Papillary formations in metastatic melanoma.

Cytomorphologic features of melanoma can be extremely variable, in that they can mimic other poorly differentiated neoplasms. Ten cases of metastatic melanoma with distinct, cohesive, papillary tissue fragments observed in fine-needle aspiration (FNA) specimens are reported. These papillary fragments exhibited a central fibrovascular core with attached tumor cells, in a background of single scattered malignant cells, macrophages, and focal necrosis. The aspiration sites included regional or distant palpable lymph nodes, pancreas, bone, and skin. Nine cases had a histologic diagnosis of primary cutaneous melanoma, and in one case the primary skin tumor was detected after the diagnosis was established by FNA of the metastasis. Immunohistochemical studies (S-100 protein, HMB-45 antigen, and factor VIII) were performed in four cases, and electron microscopy in one, confirming the diagnosis of melanoma. An awareness of this cytomorphologic variation of papillary formations in cytology preparations from metastatic melanoma is important and can prevent potential inaccurate interpretation.