Cytoplasmic and membranous receptor-binding cancer antigens expressed on SiSo cells (RCAS1) immunoreactivity in epithelial ovarian cancer cells represent differing biological function of RCAS1

Receptor-binding cancer antigen expressed on SiSo cells (RCAS1) is a selective suppressor of the immune response that has been linked to the evasion of immune surveillance by cancer cells. However, the exact prognostic impact of RCAS1 on epithelial ovarian cancer (EOC) has not been fully elucidated. The main aim of our study was to evaluate the influence of RCAS1 immunoreactivity (RCAS1-Ir) in EOC cells and in tumor stroma cells on patient overall survival. We also focused on RCAS1-Ir and the structure of the tumor stroma. RCAS1-Ir was evaluated by means of immunohistochemistry in 67 patients with EOC. We distinguished cytoplasmic and membranous immunoreactivity patterns. We found that high cytoplasmic RCAS1-Ir in cancer cells was associated with more than a two-time shortened period of overall survival. Membranous RCAS1-Ir in cancer cells, as well as in tumor stroma macrophages and fibroblasts, did not correlate with patient survival. RCAS1-Ir in the cytoplasm of cancer cells was positively correlated with the degree of tumor stroma infiltration by fibroblasts and macrophages, but not with RCAS1-Ir in these cells. On the other hand, membranous RCAS1-Ir in cancer cells was positively correlated with RCAS1-Ir in fibroblasts and macrophages, but not with their quantity. Due to their different impacts on patient prognosis and tumor stroma structure, it seems that cytoplasmic and membranous RCAS1-Ir in EOC cells may have different biological functions.