A case in point is S100 calcium-binding protein A9 (S100A9), which is strongly upregulated in ductal carcinoma in situ of the breast [23] and overexpressed in poorly differentiated invasive breast ductal carcinoma [24], especially in the basal-like and HER2-amplified breast tumors [25]. This evidence concerns the gene S100A9 and invasive ductal breast carcinoma.