Metaplastic lipid-rich carcinoma of the breast.

A case of lipid-rich mammary carcinoma identified in a lumpectomy specimen from a 56-year-old female is presented. The tumor showed features of poorly differentiated invasive ductal carcinoma of clear-cell phenotype. Cytoplasmic lucency was mainly accounted for by the accumulation of neutral fat and, to a lesser degree, glycogen. Tinctorial properties included positivity of tumor cells with Sudan III dye and diastase-sensitive periodic acid-Schiff staining. Ultrastructural examination confirmed the presence of abundant cytoplasmic lipid droplets and some glycogen rosettes. On immunohistochemistry, most tumor cells reacted for cytokeratin, vimentin and S-100 protein, and there was focal expression of carcinoembryogenic antigen. A minority of tumor cell nuclei expressed progesterone receptors. As an additional feature, part of the lesion exhibited chondroid metaplasia. Lipid-rich carcinoma of the breast is exceedingly rare and, to our knowledge, no such example harboring metaplastic elements has been described previously.