title: Standardization for Ki-67 assessment in moderately differentiated breast cancer. A retrospective analysis of the SAKK 28/12 study.
abstract: BACKGROUND
  Proliferative activity (Ki-67 Labelling Index) in breast cancer increasingly serves as an additional tool in the decision for or against adjuvant chemotherapy in midrange hormone receptor positive breast cancer. Ki-67 Index has been previously shown to suffer from high inter-observer variability especially in midrange (G2) breast carcinomas. In this study we conducted a systematic approach using different Ki-67 assessments on large tissue sections in order to identify the method with the highest reliability and the lowest variability.
  
  
  METHODS
  Five breast pathologists retrospectively analyzed proliferative activity of 50 G2 invasive breast carcinomas using large tissue sections by assessing Ki-67 immunohistochemistry. Ki-67-assessments were done on light microscopy and on digital images following these methods: 1) assessing five regions, 2) assessing only darkly stained nuclei and 3) considering only condensed proliferative areas ('hotspots'). An individual review (the first described assessment from 2008) was also performed. The assessments on light microscopy were done by estimating. All measurements were performed three times. Inter-observer and intra-observer reliabilities were calculated using the approach proposed by Eliasziw et al. Clinical cutoffs (14% and 20%) were tested using Fleiss' Kappa.
  
  
  RESULTS
  There was a good intra-observer reliability in 5 of 7 methods (ICC: 0.76-0.89). The two highest inter-observer reliability was fair to moderate (ICC: 0.71 and 0.74) in 2 methods (region-analysis and individual-review) on light microscopy. Fleiss'-kappa-values (14% cut-off) were the highest (moderate) using the original recommendation on light-microscope (Kappa 0.58). Fleiss' kappa values (20% cut-off) were the highest (Kappa 0.48 each) in analyzing hotspots on light-microscopy and digital-analysis. No methodologies using digital-analysis were superior to the methods on light microscope.
  
  
  CONCLUSIONS
  Our results show that all methods on light-microscopy for Ki-67 assessment in large tissue sections resulted in a good intra-observer reliability. Region analysis and individual review (the original recommendation) on light-microscopy yielded the highest inter-observer reliability. These results show slight improvement to previously published data on poor-reproducibility and thus might be a practical-pragmatic way for routine assessment of Ki-67 Index in G2 breast carcinomas.
authors.affiliation: Institute of Surgical Pathology, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Zsuzsanna
authors.initials: Z
authors.lastname: Varga
authors.affiliation: Swiss Group for Clinical Cancer Research, Bern, Switzerland.
authors.forename: Estelle
authors.initials: E
authors.lastname: Cassoly
authors.affiliation: Swiss Group for Clinical Cancer Research, Bern, Switzerland.
authors.forename: Qiyu
authors.initials: Q
authors.lastname: Li
authors.affiliation: Institute of Pathology, Cantonal Hospital St. Gallen, St. Gallen, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Oehlschlegel
authors.affiliation: Institute of Pathology, University Bern, Bern, Switzerland.
authors.forename: Coya
authors.initials: C
authors.lastname: Tapia
authors.affiliation: Pathology Institute Friedrichshafen, Friedrichshafen, Germany.
authors.forename: Hans Anton
authors.initials: HA
authors.lastname: Lehr
authors.affiliation: Swiss Group for Clinical Cancer Research, Bern, Switzerland.
authors.forename: Dirk
authors.initials: D
authors.lastname: Klingbiel
authors.affiliation: Swiss Group for Clinical Cancer Research, Bern, Switzerland; Breast Center, Cantonal Hospital St. Gallen, St. Gallen, Switzerland.
authors.forename: Beat
authors.initials: B
authors.lastname: Thürlimann
authors.affiliation: Breast Center, Cantonal Hospital St. Gallen, St. Gallen, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Ruhstaller
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000032:analysis*; D001940:Breast / Q000378:metabolism / Q000473:pathology*; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology*; D018270:Carcinoma, Ductal, Breast / Q000378:metabolism / Q000473:pathology*; D049109:Cell Proliferation; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D019394:Ki-67 Antigen / Q000032:analysis*; D008875:Middle Aged; D008940:Mitotic Index; D015588:Observer Variation; D012015:Reference Standards; D015203:Reproducibility of Results; D012189:Retrospective Studies
chemical_list: D014408:Biomarkers, Tumor; D019394:Ki-67 Antigen