The proteasome subunit PSMA7 located on the 20q13 amplicon was found to be differentially expressed in colorectal cancer by semiquantitative RT-PCR. PSMA7 mRNA was overexpressed in 37.5% (12/32) colorectal cancer tissues while it was either of a low level or not expressed in matched normal mucosa. The aim of this study was to examine the PSMA7 protein expression in 62 colorectal cancer primary sites, 34 lymph node metastatic sites and 13 liver metastatic sites by immunohistochemistry and clarify the correlations of this expression with the clinicopathological parameters. PSMA7 high expression was detected in 38.8% (24/62) colorectal cancer primary sites, 52.9% (18/34) lymph node metastatic sites and 100% (13/13) liver metastatic sites but not in the normal colorectal tissues. The PSMA7 high expression was significantly correlated with liver metastasis (P=0.028). Survival was significantly lower in patients with a PSMA7 high expression than in those with a PSMA7 low expression (P=0.0012). Moreover, in multivariate analysis, the PSMA7 expression demonstrated an independent prognostic factor (P=0.004, relative risk 5.057; 95% confidence interval, 1.682-15.201). These results indicated that PSMA7 may play an important role in colorectal cancer progression and provide a unique target site for the development of therapeutic drugs. The evaluation of PSMA7 expression in primary colorectal cancer at the time of surgery may be a valuable tool for defining patients with a high risk of developing liver metastasis.

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