Fine-needle aspiration biopsy of metaplastic carcinoma of the breast: report of a case with abundant myxoid ground substance.

Metaplastic carcinoma (MC) is an uncommon neoplasm of the breast. There are several variants of MC depending on the dominant histologic pattern. The components include over infiltrating ductal carcinoma, extensive squamous differentiation and spindle cell proliferation with or without chondroid or asseous heterologous elements. In FNA smears, only 57% of cases show both ductal carcinoma and metaplastic component. Thus, in almost one half of the cases, the diagnosis is not possible by FNA. Often it is difficult to define the epithelial or sarcomatous character of malignant cells. We describe a case of metaplastic carcinoma of the breast studied by fine-needle aspiration cytology in which myxoid ground substance was the dominant feature in the cytology smears. The rest of the material was composed of scanty isolated atypical cells with large and irregular nuclei. It is important to bear in mind the diagnosis of MC and make a careful search for atypical cells when the cytological smears are mainly composed of myxoid ground substance.