Ki67, also known as MKI67, is best known as the leading marker of cellular proliferation. Ki67 is regulated by a balance between synthesis and degradation, and often carries a very short half-life. First discovered to be located to dividing cells, Ki67 has since been specifically localized to the G1, S, G2 and M phases of mitosis. Soon after, it was discovered that there was a high correlation of Ki67 alongside the p53 (tumor suppressing protein 53), suggesting an implication in cancer. What’s more, the expression of Ki67 is higher in malignant cells versus control cells.