| Background | Ki-67 antigen is the prototypic cell cycle related nuclear protein, expressed by proliferating cells in all phases of the active cell cycle (G1, S, G2 and M phase). It is absent in resting (G0) cells. The monoclonal antibody is useful in establishing the cell growing fraction in neoplasms (immunohistochemically quantified by determining the number of Ki67-positive cells among the total number of resting cells = Ki67 index). In neoplastic tissues the prognostic value is comparable to the tritiated thymidine-labeling index. The correlation between low Ki67 index and histologically low-grade tumors is strong. |