Expression of RCAS1 in esophageal squamous cell carcinoma is associated with a poor prognosis

Background: Receptor-binding cancer antigen expressed on SiSO cells (RCAS1) has been reported to act as a ligand for a receptor present on normal peripheral lymphocytes and to induce apoptotic cell death. We aimed to elucidate the significance of RCAS1 expression in human esophageal squamous cell carcinomas (ESCC). Methods: RCAS1 expression was examined immuohistochemically in surgically resected esophageal carcinoma tissues from 114 patients. We also examined the relationships between RCAS1 expressions, the tumor Ki-67 indices (a marker of proliferation), and the number of CD8(+) tumor-infiltrating lymphocytes (TILs). Results: RCAS1 immunoreactivity was detected in the membranes and cytoplasm of the tumor cells. Of the 114 esophageal carcinomas, 39 (134.2%) were strongly positive for RCAS1 immunostaining on the membranes of the cancer cells, 41 (36.0%) were weakly positive, and 34 (29.8%) were negative. A comparison of RCAS1 expression and clinicopathological characteristics in all 114 patients revealed significant associations between RCAS1 expression and lymph node status (P < 0.05), and pathologic stage (P < 0.05). The survival rates of patients with RCAS1-negative tumors were significantly higher than those of patients with both RCAS1-weak positive tumors and RCAS1-strong positive ones (log-rank P < 0.05). Multivariate analysis revealed that RCAS1 positivity was an independent prognostic factor (P < 0.05). The relationship between RCAS1 expression and the numbers of CD8(+) T-cells in the primary tumors revealed that RCAS1 negative tumors tended to contain more of these cells than both RCAS1-weak positive tumors and RCAS1-strong positive ones (P = 0.2495). Conclusions: RCAS1 may play a significant role in tumor progression via an immune escape mechanism; thus, RCAS1 expression could be used as a predictor of poor prognosis in patients with ESCC. (C) 2005 Wiley-Liss, Inc.