Abstract:  Objective To investigate the expression of ribosomal S6 protein kinase type 1 （RSK1） in breast cancer and its prognostic value. Methods The RSK1 expressions in breast cancer tissues and normal breast tissues were compared based on the Protein Atlas database. The RSK1 mRNA expression data were extracted from TCGA-BRCA and GEO database，the RSK1 protein expression data were obtained from TCGA-RPPA database，to analyze the RSK1 mRNA and protein expression and its relationship with the overall prognosis of breast cancer. Results The immunohistochemical analysis of the dataset showed that the expression level of RSK1 protein in breast cancer tissues was lower than that in normal tissues. The univariable and multivariable Cox regression analysis of TCGA-BRCA database showed that the patients with high level of RSK1 mRNA had a better prognosis. The results of stratified analysis showed that female patients，age≤60 years，StageⅠ-Ⅱ，infiltrating carcinoma，no regional lymph node metastasis （N0），and no distant metastasis（M0） with high expression of RSK1 mRNA had a better prognosis. The meta-analysis results of 9 microarray datasets of GEO database was consistent with the TCGA-BRCA database（HR=0.69，95%CI：0.56-0.86，P=0.002）. The TCGA-RPPA data showed that the patients with high RSK1 protein level had a better prognosis（HR=0.49，95%CI：0.27-0.89，P=0.011），and the patients in different stages of breast cancer with high expression of RSK1 mRNA and protein were associated with better prognosis（HR=0.61，95%CI：0.39-0.95，P=0.025；HR=0.43，95%CI：0.22-0.84，P=0.008）. Conclusions High expression of RSK1 is associated with a better overall prognosis of breast cancer patients，and RSK1 can be a biomarker to predict the overall prognosis for breast cancer，especially for patients at early stage.

Key words: Breast cancer, RSK1, Prognosis, Biomarker, Bioinformatics