To assess the clinical relevance between S100A6 and MDM2 in breast cancer patients, especially that between the expression of S100A6 and chemotherapy efficacy, immunohistochemistry was performed on tumor tissues in a cohort of 107 invasive breast cancer patients receiving neoadjuvant chemotherapy with epirubicin and cyclophosphamide followed by docetaxel (EC-T). Here, S100A6 is linked to breast cancer.