Objective Primary peritoneal carcinosarcomas are similar to ovarian carcinomas in that they can metastasize by intraperitoneal dissemination; therefore, invasion of the submesothelial interstitial (stromal) matrix is an integral part of the pathology. Our objective was to study cell–matrix interactions that may influence invasive behavior of a novel, primary peritoneal carcinosarcoma cell line (PC880), and to assess how these cell–matrix interactions are different from frequently studied cultured ovarian carcinoma cells NIH:OVCAR-3, SKOV-3, and ES-2. We also wanted to determine how the expression of the cell–cell adhesion molecule E-cadherin is related to invasive behavior. Methods The PC880 cell line was established from ascites fluid of a patient diagnosed with primary peritoneal carcinosarcoma. Adhesion assays were done in titer plates coated with individual matrix components. Cell migration in monolayer cultures was assessed by the scratch wound assay method. Invasion assays were done using a three-dimensional type I collagen gel. Cytokeratin, vimentin, and E-cadherin were detected by Western blotting. E-cadherin mRNA was detected by RT-PCR. Results PC880 cells adhered well to fibronectin, laminin, and vitronectin in an integrin-dependent manner. The cells also adhered to type I collagen and invaded a three-dimensional type I collagen matrix. The invasiveness of the PC880 cells was moderated by pretreatment of the collagen matrix with heparin or chondroitin sulfate (82 and 63% of control invasiveness, respectively), indicating a role of cell surface proteoglycans in promoting invasive phenotype. Treatment of PC880 cells with sodium chlorate also decreased invasiveness (80% of control), further confirming the role of cell surface proteoglycans. Treatment of PC880 cells with function-blocking antibody to α2 integrin decreased invasiveness (57% of control), indicating the role of integrins in promoting the invasive phenotype. The protease inhibitors GM6001, E-64, and AEBSF decreased invasiveness (35, 57, and 37% of control, respectively) of PC880 cells. The ES-2 cells also adhered to type I collagen, and invaded the three-dimensional type I collagen matrix; however, inhibitors such as heparin, chondroitin sulfate, function-blocking antibody to α2 integrin, E-64, and AEBSF were less effective in moderating the invasiveness. Inhibition of invasiveness with sodium chlorate was the same as in PC880 cell, while GM6001 did not inhibit invasiveness at all. The NIH:OVCAR-3 and SK-OV-3 cells were previously found to adhere to type I collagen, but these cells did not invade the three-dimensional type I collagen matrix. In a monolayer culture PC880 and ES-2 cells had significantly higher motility than NIH:OVCAR-3 and SK-OV-3 cells. Only these noninvasive cell lines expressed E-cadherin protein or mRNA. Conclusions PC880 is the first cell line established from primary peritoneal carcinosarcoma, and the cytoskeletal composition indicated that these cells represent the sarcomatous elements of the tumor. PC880 cells, similar to ES-2 cells, adhered to type I collagen, and invaded a three-dimensional collagen matrix. The invasion of the interstitial matrix by both the peritoneal carcinosarcoma and the ovarian carcinoma cell line was mediated by cell surface proteoglycans, α2 integrin, and proteases. The invasive cell behavior of PC880 and ES-2 cells correlated with a high degree of motility, and with the lack of expression of the cell–cell adhesion molecule E-cadherin.