The validation studies showed that the expression of S100A8 was at high levels in MDA-MB-231 (79.7%), MDA-MB-453 (89.2%), HTB-9 (70.2%), and T24 (53.3%) cells and it was higher in breast cancer tissue and bladder cancer tissue than their corresponding para-carcinoma tissue.<h4>Conclusions</h4>S100A8 overexpression was significantly associated with poor clinical prognosis in cancer patients. This evidence concerns the gene S100A8 and breast cancer.