Objective   To investigate the expression of STEAP1 in human breast cancer and its clinical significance.

  Methods   Immunohistochemical staining was performed to detect the expression of STEAP1 in breast tissues from 40 normal women, 52 patients with breast fibroadenoma, and 211 patients with breast cancer in Qianfo Hill Hospital of Shandong Province from January 2007 to December 2016. According to the expression level of STEAP1, the breast cancer patients were assigned into high and low expression groups. Clinical pathological characterization and Kaplan-Meier survival analysis of the two groups were performed. RT-PCR and Western blot were conducted to measure the expression of STEAP1 in mammary gland cells. The Oncomine and Kaplan-Meier Plotter databases were used to analyze the expression and prognosis of STEAP1.

  Results   Immunohistochemistry showed that the high expression rate of STEAP1 in breast cancer was 11.8% (25/211), which was significantly lower (P < 0.001) than that in normal breast (85.0%, 34/40) and fibroadenoma (84.6%, 44/52). The result was consistent with the Oncomine database analysis that the expression in breast cancer tissue was lower than that in normal breast tissue. RT-PCR and Western blot analyses showed that the mRNA and protein expression levels of STEAP1 were significantly higher in mammary epithelial cells than in MDA-MB-468, BT549 and MCF-7 breast cancer cell lines, and a significant difference was found among the four types of cells (P < 0.001). Kaplan-Meier survival analysis and Kaplan-Meier Plotter database analysis showed that patients with high STEAP1 expression had better prognosis than those with low STEAP1 expression (P < 0.05).

  Conclusion  The expression level of STEAP1 in normal breast was higher than that in breast cancer. High STEAP1 expression is associated with a better prognosis.