In this study of 203 cases of invasive cancer, we took advantage of a recently established polyclonal antibody specifically recognising YKL-40 to evaluate the expression of YKL-40 in different breast tissues including benign breast tissue, breast ductal carcinoma in situ (DCIS), and invasive ductal carcinoma (IDC) using an immunohistochemical (IHC) assay. The gene discussed is CHI3L1; the disease is ductal breast carcinoma in situ.