AbstractProtease activated receptors (PAR) form a family of G‐protein coupled receptors (GPCR) encoding their own ligands and uniquely activated via proteolytic cleavage. Although proteases in general have been implicated in the remodeling of the extracellular tumor microenvironment, the role of cell surface receptors activated by proteolysis is now emerging. In our present study we investigated the expression pattern of protease activated receptor 1 hPar1 in ovarian carcinoma tissue samples. Abundant hPar1 mRNA and protein were detected in “low malignant potential” and in invasive carcinomas, regardless of the histological subtype. In contrast, no hPar1 expression was detected on the cell surface of normal ovarian epithelium. The differential expression pattern of hPar1 was shown by in situ hybridization, immunohistochemistry and semi‐quantitative RT‐PCR analyses. In early stages of ovarian carcinoma (Ia), the contra lateral normal ovary showed strong PAR1 expression as opposed to the lack of expression in the ovarian epithelium obtained from normal individuals. In parallel, we analyzed the expression pattern of αvβ5 integrin and of activated focal adhesion kinase (FAK), a major focal contact protein, in these tissues. Although abundant expression of αvβ5 integrin was observed in all tissues specimens examined, regardless of either normal or malignant, the level of activated FAK was differentially expressed. Phosphorylated FAK was seen in invasive ovarian carcinoma, but not in the normal ovarian epithelium. The abundant hPar1 levels in pathological malignant ovarian carcinoma is likely to transmit signals leading to the phosphorylation of FAK and thereby alterations in the integrin functional state. Altogether our data suggest that hPar1 and FAK cooperate to promote ovarian cancer malignancy.