THE UROKINASE RECEPTOR IS EXPRESSED IN INVASIVE BREAST-CANCER BUT NOTIN NORMAL BREAST-TISSUE

We have studied expression of the urokinase receptor (u-PAR) in paraff in-embedded breast tissues at various stages of malignant progression. Forty-nine of 59 invasive cancers studied showed varying degrees of r eactivity with our polyclonal antibody. The staining pattern was varia ble from case to case, although strong surface staining of tumor-assoc iated macrophages was evident in most of these sections. In several ca ses, blood vessels in selected tumor areas were stained, as confirmed by treatment of adjacent sections with an anti-factor Vm antibody. The se could represent regions of recent angiogenesis. Staining of tumor c ells was observed in 21 of 59 cases and was extensive in 5 cases but c onfined to a small percentage of cells in the remaining 16 samples. In contrast with the cancer sections, all normal breast tissue (12 cases ) was negative, as well as all fibroadenomas (4 cases), papillomas (5 cases), and hyperplasia with atypia (2 cases) studied. Seven carcinoma s in situ examined were also negative for u-PAR, with the exception of few macrophages in two cases, suggesting that u-PAR expression may be associated with invasive tumor. The presence of u-PAR in human breast cancer and its absence from nonmalignant breast tissue supports the i dea that plasminogen activation plays an important role in the process of cancer invasion. Expression of u-PAR on macrophages, endothelial c ells, and cancer cells suggests the existence of complex paracrine int eractions between tumor cells and stroma.