The extracellular matrix in sarcomatoid carcinomas of the breast.

The distribution of the main extracellular matrix components has been investigated immunohistochemically in four cases of breast sarcomatoid carcinomas. The histogenesis of these tumours is still unclear, but most evidence suggests that the sarcomatous component originates from mesenchymal conversion of carcinomatous cells. We found that carcinomatous portions of the tumours were associated with linear basement membrane-like deposition of laminin, type IV collagen and heparan sulphate proteoglycan that partially circumscribed the epithelial nests. The sarcomatous components produced an extracellular matrix immunoreactive to fibronectin, type I, III and VI collagens and tenascin. However, in two cases, in some sarcomatous areas, focal pericellular staining for antibodies to laminin and type IV collagen was seen. These results indicate that modifications observed in the double tissue component of these tumours involve not only the cell shape and the cytoskeleton, but also the components of the extracellular matrix. The significance of these findings and their relevance in the understanding of the phenotypic pattern changes of these biphasic tumours are discussed.