Ultrastructural and immunohistochemical characteristics of lipid-rich carcinoma of the breast.

Five cases of lipid-rich carcinomas of the breast were investigated ultrastructurally and immunohistochemically for alpha-lactalbumin (ALA), lactoferrin (Lfr) and human milk fat globule membrane antigen (HMFG-2). Staining for ALA and Lfr showed intensive reaction on nearly all of the tumour cells whereas immunoreaction for HMFG-2 revealed positivity in single cells. All tumours were negative for steroid receptor content. Ultrastructurally the tumour cells showed numerous intracytoplasmic non-membrane bound lipid droplets which were often found within autophagocytic vacuoles. Neither rough endoplasmic reticulum nor Golgi complexes showed any sign of lipid synthesis. Extrusion of lipid droplets and extracellular lipid deposition was not observed. In conclusion, our findings do not justify the consideration of lipid-rich carcinoma of the breast as a clearly defined group of tumours with specific secretory activity. Therefore, the term lipid-rich carcinoma should be used in preference to lipid-secreting, unless there is evidence of active lipid secretion.