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International Ki67 in Breast Cancer Working Group

The Ki67 proliferation biomarker may be useful to assess prognosis, predict response to chemotherapy and endocrine therapy, estimate residual risk in patients, and determine treatment efficacy in breast cancer. However, variations in methodologies for Ki67 measurement have resulted in variations among laboratory results, limiting the clinical utility of this biomarker. Many Ki67 experts, designated as the International Ki67 in Breast Cancer Working Group, convened at the Breakthrough Breast Cancer Research Center (London) on March 12, 2010, to review the existing methodologies and propose guidelines to reduce such variations. In a commentary, Dowsett et al. (p. 1656 ) , and the International Ki67 in Breast Cancer Working Group experts, provide a comprehensive overview of methodologies, identify problem areas, and provide recommendations for the preanalytical and analytical validity of Ki67, interpretation of its staining and scoring, and data handling. The authors have initiated a pilot quality assessment scheme for researchers to help reduce inter-laboratory variability.