The Ki-67 proliferation index (PI), which is determined by immunohistochemical staining, has prognostic and predictive value in several cancers including pulmonary neuroendocrine tumors (3), pulmonary adenocarcinoma (PAD) (4), and breast ductal carcinoma (BDC) (5). This evidence concerns the gene MKI67 and breast ductal adenocarcinoma.