Inter-laboratory and inter-observer reproducibility of immunohistochemical assessment of the Ki-67 labelling index in a large multi-centre trial

J Pathol. 2002 Nov;198(3):292-9. doi: 10.1002/path.1218.


Proliferative activity of tumour cells, as assessed by the Ki-67 labelling index, has been suggested as a potential prognostic indicator in many neoplastic diseases. Meaningful application of the immunohistochemically determined tumour cell growth fraction in clinical decision-making requires information about its inter-laboratory reproducibility. To assess the reproducibility of Ki-67 determined growth fraction, a multi-centre immunohistochemical trial was performed with 172 participating laboratories, each testing 30 different tissue samples. Evaluating 5160 Ki-67 labelling indices with a newly developed tissue microarray, good inter-observer reproducibility but high inter-laboratory variability was found. Reassessment of all stainings revealed considerable inter-laboratory differences in the intensity and frequency of labelled nuclei, suggesting that antigen retrieval or staining techniques are predominantly responsible for the inter-laboratory variability found in this trial. Consequently, cut-off levels for Ki-67, suggested to distinguish prognostic subgroups in tumours, appear to have limited reproducibility in a multi-centre approach. It is concluded that there is a need to standardize the immunohistochemical determination of the Ki-67 labelling index when it is used as a prognostic indicator in surgical pathology.

Publication types

  • Clinical Trial
  • Multicenter Study

MeSH terms

  • Biomarkers, Tumor / analysis*
  • Breast Neoplasms / pathology*
  • Cell Division
  • Female
  • Histocytological Preparation Techniques / standards*
  • Humans
  • Immunohistochemistry
  • Ki-67 Antigen / analysis*
  • Observer Variation
  • Oligonucleotide Array Sequence Analysis / methods
  • Prognosis
  • Quality Assurance, Health Care*
  • Reproducibility of Results
  • Staining and Labeling / methods
  • Tissue Fixation / methods


  • Biomarkers, Tumor
  • Ki-67 Antigen