Ki67 as a Biomarker of Prognosis and Prediction: Is it Ready for Use in Routine Pathology Practice?

Breast cancer is the most common cancer in women, and the search for effective markers to design therapeutic strategies and patient management algorithms is still a work in progress. Ki67, a proliferative marker, has gained attention as a prognostic and predictive factor in early breast cancer and/or to decide response to chemotherapy. Individual studies and meta-analyses have provided evidence of its usefulness in this regard. Immunohistochemical staining Ki67 has emerged as an easy and cheap tool to assess proliferation in laboratory setting. However, debate continues over its meaningful clinical use, given the lack of standardization of staining techniques and firm recommendations about pre-analytical tissue handling, interpretation of the stain, and methods to estimate Ki67, resulting in high interlaboratory and interobserver variability. Importantly, no consensus has been reached on the cut-off values for risk stratification. The Breast Cancer Working Group proposed guidelines for immunohistochemical evaluation of Ki67 in 2011. However, the follow-up study showed poor reproducibility even among experts, and the use of Ki67 in daily practice is still in question.