Ki67 protein is a non-histone nuclear protein encoded by the MKI67 gene, widely used as a proliferation marker in pathology. It is expressed during all active phases of the cell cycle鈥擥1, S, G2, and M鈥攂ut is absent in quiescent (G0) cells. Ki67 has multiple molecular functions, including forming the perichromosomal layer to prevent chromosome aggregation during mitosis and organizing heterochromatin. It also facilitates chromosome attachment to the mitotic spindle and individual chromosome mobility. In addition to its role in cell division, Ki67 is a valuable prognostic and predictive indicator in cancer diagnosis, with its expression levels correlating with tumor cell proliferation rates.