title: Validity of whole slide images for scoring HER2 chromogenic in situ hybridisation in breast cancer.
abstract: Whole slide images (WSIs) have stimulated a paradigm shift from conventional to digital pathology in several applications within pathology. Due to the fact that WSIs have not yet been approved for primary diagnostics, validating their use for different diagnostic purposes is still mandatory. The aim of this study was to test the validity of WSI in assessing human epidermal growth factor receptor 2 (HER2) status in breast cancer specimens using chromogenic in situ hybridisation (CISH).
  
  
  
  Ninety-six HER2 CISH slides were scored by two observers on a light microscope (400× viewing magnification) and on WSI (40× scanning magnification, one focus plane) with a minimum of 6 weeks washout period. The concordance between digital and microscopic HER2 scores was assessed.
  
  
  
  Digitally, 93/96 cases could be assessed (96.8%). Microscopic and digital evaluation of HER2 amplification status were concordant in 68/93 cases ((73.1%, 95% CI: 0.639 -0.823), κ 0.588). CISH underscoring was most noticeable in the amplified and equivocal categories while the highest level concordance was seen in cases with a normal copy number. Additionally there was a noticeable tendency to underestimate the average HER2 scores on WSI: lower in 59 and higher in 11 cases. There was no major difference in time spent for microscopic scoring (86.9 s) and digital scoring (81.7 s).
  
  
  
  There was a reasonable concordance between microscopic scoring and WSI-based scoring of HER2 copy number of CISH slides. Nevertheless, WSIs scanned on a single focal plane are insufficient to assess HER2 gene amplification status by scoring CISH due to the noticeable tendency towards digitally underestimating the number of HER2 spots. Scanning at multiple focus planes may offer better resolution for improved digital CISH spot counting.
authors.affiliation: Symbiant Pathology Expert Center, Alkmaar, The Netherlands.
authors.forename: Shaimaa
authors.initials: S
authors.lastname: Al-Janabi
authors.affiliation: Symbiant Pathology Expert Center, Alkmaar, The Netherlands.
authors.forename: Anja
authors.initials: A
authors.lastname: Horstman
authors.affiliation: Symbiant Pathology Expert Center, Alkmaar, The Netherlands.
authors.forename: Henk-Jan
authors.initials: HJ
authors.lastname: van Slooten
authors.affiliation: Symbiant Pathology Expert Center, Alkmaar, The Netherlands.
authors.forename: Chantal
authors.initials: C
authors.lastname: Kuijpers
authors.affiliation: Symbiant Pathology Expert Center, Alkmaar, The Netherlands.
authors.forename: Clifton
authors.initials: C
authors.lastname: Lai-A-Fat
authors.affiliation: Department of Pathology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: van Diest
authors.affiliation: Symbiant Pathology Expert Center, Alkmaar, The Netherlands Department of Pathology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Jiwa
keywords: BREAST CANCER; BREAST PATHOLOGY; CANCER; DIGITAL PATHOLOGY