Prognostic value of raf kinase inhibitor protein in esophageal squamous cell carcinoma

Raf kinase inhibitory protein (RKIP, also PEBP1) is involved in regulation of multiple cellular signaling processes and suppressing metastasis in animal models. Downregulation of RKIP expression has been shown to promote tumor progression in a variety of human cancers. However, its role and clinical significance in resectable esophageal squamous cell carcinoma (ESCC) is still scanty. The purpose of this study was to investigate the prognostic significance of RKIP expression by immunohistochemistry in a group of patients with ESCC treated with surgical resection. RKIP expression in 233 surgically resected ESCC specimens and 49 cases of adjacent normal tissues was detected by using immunohistochemical staining. The clinical and prognostic significance of RKIP expression was statistically analyzed. Kaplan-Meier analysis was used to compare the postoperative survival between groups. Significant downregulation was noted for RKIP protein in ESCCs, compared to adjacent normal tissues (p < 0.001). A lower disease-free survival and overall survival of ESCC was found in patients whose tissues had low RKIP expression (both P < 0.001). In addition, RKIP expression could stratify the patient survival (disease-free survival/overall survival) in stage II (P = 0.01 and 0.02, repectively). The Cox proportionate hazard regression model also established that low expression of RKIP was significantly correlated with increased risk (RR = 3.572) of recurrence compared with high RKIP expression (P < 0.001). Furthermore, the results of multivariate analysis suggested that RKIP expression (P < 0.001) was an independent factor that affected overall survival. These findings suggest that the low expression of RKIP be associated with poor survival in resectable ESCC patients.