High tissue content of urokinase plasminogen activator (u‐PA) is associated with high stromal expression of u‐PA mRNA in poorly differentiated serous ovarian carcinoma

Urokinase plasminogen activator (u‐PA) plays a pivotal role in tissue degradation during tumor spread and metastasis. We have quantitated u‐PA in tissue homogenates of 31 serous ovarian tumors and localized u‐PA and its mRNA in tissue sections of 26 serous ovarian tumors. The content of u‐PA was higher in malignant than in benign tumors, with the highest levels being found in poorly differentiated cancers. In tissue sections, the u‐PA mRNA was hybridized with a radiolabeled RNA probe. Signals were almost exclusively found in the epithelium in benign and borderline tumors and in well‐differentiated cancers. Poorly differentiated tumors and metastases exhibited prominent stromal expression of u‐PA mRNA, whereas epithelial expression was weak or absent. Immuno‐histochemical staining co‐localized u‐PA antigen with its mRNA in the epithelium of benign and borderline tumors and in well‐differentiated cancers. Poorly differentiated malignant tumors showed extensive immunostaining in the epithelium in addition to stromal staining. The u‐PA mRNA‐expressing and u‐PA‐immunostained cells in the stroma were not tumor cells since no cells in the stroma were positive for cytokeratin. Poorly differentiated tumors had increased numbers of stromal macrophages (CD68), and they co‐localized with some of the u‐PA‐positive cells. The presence of u‐PA antigen and the absence of u‐PA mRNA in tumor epithelium of poorly differentiated tumors and metastases together with the presence of u‐PA mRNA in the stroma suggests production in stromal cells and subsequent binding to receptor sites in tumor cells. Int. J. Cancer (Pred. Oncol.) 79:588–595, 1998. © 1998 Wiley‐Liss, Inc.