Fibronectin: a discrimination marker between small invasive carcinomas and benign proliferative lesions of the breast.

The connective tissue glycoprotein, fibronectin (FN) is known to be increased in the stromal desmoplastic response associated with invasive breast carcinoma (IBC). In a previous study of 77 IBCs we found that all tumours, irrespective of desmoplasia, displayed an intense stromal immunoreactivity for FN, although those with a high metastatic potential tended to lack this in foci along their infiltrating border (Christensen et al. 1988). In order to test the diagnostic value of this observation, FN immunoreactivity was estimated semiquantitatively in 131 small primary IBCs, 23 in situ carcinomas, 20 borderline lesions, 142 benign proliferative breast lesions and 35 samples of normal breast tissue. All IBCs, including those without apparent desmoplasia, were accompanied by an intense stromal staining for FN forming a diffuse or pericellular pattern around the tumour cells (FN positive reaction). This was not seen in the benign lesions (FN negative reaction) with the exception of an FN positive, linear staining around some cysts and ectatic ducts and a diffuse staining of the connective tissue core of some intraductal papillomas. Intraductal carcinomas, multiple papillomas and radial scars could display a substantial staining for FN, sometimes enclosing small islands or tubules of epithelial cells. However, the fact that all IBCs of this study produced an overall reliable and consistent FN positive stromal reaction, which was only interrupted in minute foci along the infiltrating border in a few of the largest tumours (11/131), makes immunohistochemical staining for FN an excellent adjunct to morphology in tracing small, primary IBCs.