Practical Issues of Ki-67 Evaluation in Breast Cancer Clinical Practice

Abstract

For the past several decades, markers of cellular proliferation in breast cancer have been postulated to indicate prognosis and predict benefits from antineoplastic therapies. The most common method to measure cellular proliferation by Ki-67 is immunohistochemistry (IHC) based assays. However, analytical issues have hindered the widespread adoption of these measures in patient care. The recent monarch E clinical trial prospectively investigated Ki-67 as a biomarker of cyclin-dependent kinase inhibitor (CDKI), Abemaciclib in the adjuvant setting. It established the benefit of CDKI in high-risk ER-positive breast cancer patients with Ki-67 expression >20%, which promoted the increased clinical demand for routine Ki-67 testing in pathology laboratories. This review summarizes some recent developments and practical issues for Ki-67 evaluation.