title: Observer performance in the use of digital and optical microscopy for the interpretation of tissue-based biomarkers.
abstract: BACKGROUND
  We conducted a validation study of digital pathology for the quantitative assessment of tissue-based biomarkers with immunohistochemistry.
  
  
  OBJECTIVE
  To examine observer agreement as a function of viewing modality (digital versus optical microscopy), whole slide versus tissue microarray (TMA) review, biomarker type (HER2 incorporating membranous staining and Ki-67 with nuclear staining), and data type (continuous and categorical).
  
  
  METHODS
  Eight pathologists reviewed 50 breast cancer whole slides (25 stained with HER2 and 25 with Ki-67) and 2 TMAs (1 stained with HER2, 1 with Ki-67, each containing 97 cores), using digital and optical microscopy.
  
  
  RESULTS
  Results showed relatively high overall interobserver and intermodality agreement, with different patterns specific to biomarker type. For HER2, there was better interobserver agreement for optical compared to digital microscopy for whole slides as well as better interobserver and intermodality agreement for TMAs. For Ki-67, those patterns were not observed.
  
  
  CONCLUSIONS
  The differences in agreement patterns when examining different biomarkers and different scoring methods and reviewing whole slides compared to TMA stress the need for validation studies focused on specific pathology tasks to eliminate sources of variability that might dilute findings. The statistical uncertainty observed in our analyses calls for adequate sampling for each individual task rather than pooling cases.
authors.affiliation: Division of Imaging, Diagnostics, and Software Reliability, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, MD 20993, USA.
authors.forename: Marios A
authors.initials: MA
authors.lastname: Gavrielides
authors.affiliation: Laboratory of Pathology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA ; Leica Biosystems, Vista, CA 92081, USA.
authors.forename: Catherine
authors.initials: C
authors.lastname: Conway
authors.affiliation: Division of Imaging, Diagnostics, and Software Reliability, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, MD 20993, USA.
authors.forename: Neil
authors.initials: N
authors.lastname: O'Flaherty
authors.affiliation: Division of Imaging, Diagnostics, and Software Reliability, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, MD 20993, USA.
authors.forename: Brandon D
authors.initials: BD
authors.lastname: Gallas
authors.affiliation: Laboratory of Pathology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Hewitt
mesh_terms: D014408:Biomarkers, Tumor / Q000032:analysis*; D001943:Breast Neoplasms / Q000175:diagnosis; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D007150:Immunohistochemistry; D008853:Microscopy / Q000379:methods*; D015588:Observer Variation; D010338:Pathology, Clinical / Q000379:methods* / Q000592:standards*; D046888:Tissue Array Analysis
chemical_list: D014408:Biomarkers, Tumor