Fine needle aspiration biopsy of metastatic malignant melanoma with "rhabdoid" features. Frequency, cytologic features, pitfalls and ancillary studies.
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.


METHODS
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.
Slagel
D D
DD
Department of Pathology and Laboratory Medicine, East Carolina University School of Medicine, Greenville, North Carolina 27858-4354, USA.
Raab
S S
SS
Silverman
J F
JF
D000310:Adrenal Gland Neoplasms / Q000473:pathology; D000328:Adult; D000368:Aged; D000951:Antigens, Neoplasm; D001707:Biopsy, Needle; D003937:Diagnosis, Differential; D006801:Humans; D007150:Immunohistochemistry; D007633:Keratins / Q000032:analysis; D008175:Lung Neoplasms / Q000473:pathology; D008223:Lymphoma / Q000473:pathology; D008297:Male; D008545:Melanoma / Q000737:chemistry / Q000276:immunology / Q000473:pathology*; D058950:Melanoma-Specific Antigens; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000032:analysis; D012189:Retrospective Studies; D009418:S100 Proteins / Q000032:analysis; D014746:Vimentin / Q000032:analysis
D000951:Antigens, Neoplasm; D058950:Melanoma-Specific Antigens; D009363:Neoplasm Proteins; D009418:S100 Proteins; D014746:Vimentin; D007633:Keratins