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Fine needle aspiration biopsy of metastatic malignant melanoma with "rhabdoid" features. Frequency, cytologic
D D Slagel1, S S Raab, J F Silverman
1Department of Pathology and Laboratory Medicine, East Carolina University School of Medicine, Greenville, North Carolina 27858-4354, USA.
Objective:
To characterize the cytopathology of metastatic malignant melanoma (MM) with "rhabdoid" features, a recently described, rare morphologic variant of MM that can be incorrectly diagnosed in fine needle aspiration (FNA) biopsy.
Study Design:
A retrospective review of all FNA biopsy material with the diagnosis of metastatic MM was performed at two institutions. Only cases with a predominant composition of cells that met criteria defined as "rhabdoid" morphology were selected for study. The cytomorphologic features, immunocytochemistry and clinical features of these cases were reviewed.
Results:
Of 88 FNA cases previously diagnosed as metastatic MM, 4 (4.6%) had a predominance of cells with rhabdoid features. These cases consisted of scattered atypical cells having enlarged, eccentrically placed nuclei; prominent nucleoli; and a moderate amount of cytoplasm possessing round, globular inclusions in Papanicolaou- and Diff-Quik-stained smears. Immunochemistry showed strong S-100, HMB-45 and vimentin staining in two of four cases.
Conclusions:
Metastatic MM may present in FNA biopsy as a poorly differentiated malignancy with rhabdoid features, potentially leading to an incorrect cytologic diagnosis. MM must be considered when evaluating neoplasms with a rhabdoid phenotype. Correlation of the cytologic finding with the clinical history and immunohistochemical studies can help in diagnosing this morphologic variant.