RÉSUMÉ
<p><b>OBJECTIVE</b>To study the expression and clinical significance of ribosomal S6 kinase-4 (RSK-4) in breast cancer and explore the role of RSK-4 in the genesis and development of breast cancer.</p><p><b>METHOD</b>The expression levels of RSK-4 mRNA and protein were detected in 56 cases of breast cancer and the normal breast tissues, as well as in 20 cases of breast benign lesions, by reverse transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry.</p><p><b>RESULTS</b>The expression rates of RSK-4 mRNA in breast cancer, the normal breast tissues and breast benign lesions were 48.2%, 76.8% and 75.0%, respectively. The expression level of RSK-4 mRNA in breast cancer was significantly lower than those in normal breast tissues and breast benign lesions tissues (P < 0.05). The expression level of RSK-4 significantly correlated with tumor size and clinical stage (P < 0.05).The expression rate of RSK-4 protein was 39.3% in breast cancer tissues, which was significantly lower than that of normal breast tissues (71.4%) and breast benign lesions (75.0%, P < 0.01). The expression level of RSK-4 protein was lower in breast cancer with large tumor, high clinical stage and lymph node metastasis. In 56 cases of breast cancer samples, the consistency rate of RSK-4 mRNA and protein was 73.2%. A significant correlation was found between RSK-4 mRNA and protein (χ² = 10.254, P < 0.05).</p><p><b>CONCLUSION</b>The down-regulation of RSK-4 expression in breast caner suggests that it is a breast cancer suppressor gene, and the lack or down-regulation of RSK-4 expression is involved in the genesis and progression of breast cancer.</p>