Ki-67 antigen is a nuclear antigen specifically associated with cell proliferation. Ki-67 is expressed in all proliferating cells which are in the active phases of the cell cycle (late G1, S, G2, and mitosis), but absent in resting cells. Ki-67 labeling index has been show to be elevated in early stage and further increased in advanced stage of various types of cancer including breast cancer, colon cancer, prostate cancer and brain cancer.