S100A9 and breast cancer: Authors have found that the S100 gene family, which comprises over 20 members, including S100A1, S100A2, S100A8, and S100A9 encoded low molecular weight calcium-binding proteins with important physiological and pathological roles in keratinization [26]; however, there has also been evidence of a correlation between breast cancer and S100A2, S100A4, S100A6, S100A7, S100A8, S100A9, and S100A11 [27].