〔Abstract〕 Objective To investigate the expression and clinical significance of AP-1 complex subunit sigma-1 A(AP1 S1) gene in breast cancer. Methods The relationship between the expression level of AP1 S1 and the clinical prognosis of breast cancer patients was analyzed using the data in surgical tissues and adjacent tissues of breast cancer patients published in the online databases of GEPIA and UALCAN. 110 cases of wax block specimens with complete clinical data and complete clinical data were collected. The expression of AP1 S1 in breast cancer tissues was detected by immunohistochemistry.In vitroexperiments were performed using plate clones, CCK-8 and cell scratch experiments to analyze the effect of AP1 S1 expression on the proliferation and metastasis characteristics of breast cancer cells. Results Through the analysis of GEPIA and UALCAN data, it was found that the expression level of AP1 S1 in breast cancer tissues was significantly higher than that in normal breast tissues(P<0.01). The expression level of AP1 S1 was significantly associated with overall survival(OS) and disease-free survival(DFS)(P<0.05), and it was closely related to the tumor stage of breast cancer patients(P<0.05), and had no obvious correlation with age, tumor classification and lymph node metastasis. Clinical case analysis confirmed that AP1 S1 expression was closely related to breast cancer tumor size and AJCC stage(P<0.05), and had no significant correlation with age, lymph node metastasis, estrogen receptor(ER) status, progesterone receptor(PR) status, and human epidermal growth factor receptor 2(HER2) status(P>0.05). The results of cell function experiments showed that the expression of AP1 S1 gene could promote the proliferation, colony formation and migration ability of breast cancer cells. Conclusion AP1 S1 gene is highly expressed in breast cancer tissues, and its expression level is related to the prognosis of breast cancer patients. Moreover, AP1 S1 gene expression can promote breast cancer cell proliferation, colony formation and migration ability.