Background: Ki-67 is a marker of cell proliferation detected in cells that are in G1-, S-, G2-, and M-phase of the cell cycle and absent in cells in G0. Ki-67 is detected exclusively in the nucleus, and its detection by immunohistological methods has proven to have diagnostic and prognostic value in the study of a variety of human tumors. The specific cellular functions of Ki-67 have not been elucidated, but it is proposed to function in the organization and maintenance of the architecture of DNA and in the synthesis of ribosomes during mitosis.