The evaluation of cellular proliferation in breast cancer cells has been measured using several different methodological approaches, including analysis of thymidine uptake [2,3], flow cytometry to determine the percent of cells in S phase [2,4], the counting of mitotic figures, the immunohistochemical expression of Ki-67 [4,5], and through molecular multigene assays which measure genes transcripts associated with proliferation as a central component of their genomic profile (such as Oncotype DX and MammaPrint) [6,7,8]. This evidence concerns the gene MKI67 and breast cancer.