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

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).

RCAS1 expression was examined immunohistochemically 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).

RCAS1 immunoreactivity was detected in the membranes and cytoplasm of the tumor cells. Of the 114 esophageal carcinomas, 39 (34.2%) 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).

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.