Expression and prognostic significance in lung cancer of human tumor-associated antigen RCAS1

A new monoclonal antibody (MAb), 22-1-1, acts against a novel tumor-associated antigen (Ag) strongly expressed in human uterine cervical adenocarcinomas. A cDNA encoding the Ag recognized by the 22-1-1 MAb has been isolated and called RCAS1 (receptor-binding cancer antigen expressed on SiSo cells). RCAS1 can induce growth arrest and apoptosis in RCAS1 receptor-positive cells including T cells and natural killer cells in vitro. These results suggest that RCAS1 is involved in tumor escape from the immune system. Immunohistochemical analysis revealed the relationship between RCAS1 expression and clinicopathological variables (age, sex, smoking, histology, differentiation grade, pathological T factor, N factor and stage) and the prognostic significance of RCAS1 in 66 lung-cancer patients who underwent curative operations: 33 adenocarcinomas, 24 squamous-cell carcinomas, 3 large-cell carcinomas, 4 adenosquamous carcinomas and 2 small-cell carcinomas. Median follow-up period of 64 non-small-cell carcinomas (NSCLCs) was 67.4 months. RCAS1 was expressed in 74.2% of lung cancers. RCAS1 in NSCLC cases with advanced T factor or pathological stage or in poorly differentiated adenocarcinomas was highly expressed. Furthermore, RCAS1 expression inducing apoptosis of tumor-infiltrating lymphocytes was a significant prognostic factor in NSCLC (p<0.03).