Malignant melanoma in effusions: a source of false-negative cytodiagnoses

Melanoma, a not uncommon tumor, is associated with variable cytomorphology and unpredictable metastatic potential. Although most cytologic diagnoses of malignant melanoma represent metastatic disease, the diagnosis is frequently unsuspected clinically. Three effusions in which cells from metastatic melanomas were not diagnosed are described. Clinical factors that may have contributed to the erroneous cytodiagnoses are illustrated. Cytologic features and adjunctive studies that are helpful in identifying melanoma cells are discussed.