Ki-67 is an antibody that targets Ki-67 antigen-a nuclear protein encoded by the MKI67 gene, whose presence correlates with G1, S, G2 and the mitotic phases of the cell cycle.the presence of Ki-67 during cell division makes it an excellent target for labeling fast-growing malignancies. Since its presence correlates with cell proliferation, immunohistochemical labeling of Ki-67 antigen can be useful to characterize the growth fraction of a lesion. Identification of this antigen by IHC has been shown to be useful in characterizing lesions of the breast, lymphoid cells, astrocytes and uterus.