Immunohistochemical staining patterns of tenascin in invasive breast carcinomas.

Eighty-two cases of primary invasive breast carcinoma and adjacent "normal" mammary glands were examined immunohistochemically for tenascin expression and distribution. Formalin-fixed tissues pretreated with actinase were processed by the avidin-biotin complex method using anti-human tenascin monoclonal antibody (RBC1). In normal mammary glands, tenascin was distributed around the ducts and ductules but not around the acini. In carcinomas, a high incidence of tenascin-positive cases (greater than 67%) was seen with various histological appearances, with the exception of lobular carcinoma where a low incidence was found (25%). Although intense staining was seen around cancerous foci when compared with normal mammary glands, tenascin was often expressed at cancer-mesenchymal junctions with dense fibrotic stroma, but not at junctions with active inflammatory change and a loose fibrotic stroma. Tenascin, expression is not an all-or-none marker for mammary malignancy and the staining pattern suggests either a role in stimulating cancer cells or a host defence mechanism accompanied by a desmoplastic response to them.