Reduced expression of erythropoietin-producing hepatocyte B6 receptor tyrosine kinase in prostate cancer.

Loss of erythropoietin-producing hepatocyte (Eph) B6 gene expression is associated with poor prognosis in neuroblastoma, melanoma and other tumors. The present study evaluated the expression of EphB6 receptor tyrosine kinase in normal and prostate cancer tissue using immunohistochemistry. The association between EphB6 expression, clinicopathological findings, proliferating-cell nuclear antigen (PCNA; another prognostic marker) and progression of prostate cancer was analyzed. Tissue microarray samples of normal prostatic tissue and prostate cancer tissue from 46 patients treated with radical prostatectomy for prostate cancer were included in this study. Polyclonal anti-EphB6 and monoclonal anti-PCNA antibodies were used to assess EphB6 and PCNA expression by immunohistochemistry. EphB6 was expressed in normal and prostate cancer tissue; however, its expression was significantly reduced in prostate cancer tissue compared with normal prostatic tissue (P<0.0001), in high volume (≥4 cm) cancer compared with low volume (<4 cm; P=0.015), and in pT3 stage compared with pT2 stage of the disease (P=0.0007). No correlation was observed between the expression of EphB6 and PCNA. Short biochemical progression-free survival was associated with low EphB6 protein expression (P=0.157). This study revealed that EphB6 may have a tumor suppressor effect in prostate cancer, at least during early stages of this disease. This provides new insight into the potential utility of EphB6 receptor as a diagnostic/prognostic marker for prostate cancer.