Reading immunohistochemical slides on a computer monitor--a multisite performance study using 180 HER2-stained breast carcinomas.

Background: With the adoption of digital pathology, image analysis (IA) of immunohistochemistry (IHC) slides can be integrated seamlessly into the digital pathology workflow. A pathologist can now use IA efficiently while reading the digital IHC slides on a computer monitor. Thus, the clinical acceptance of a digital pathology system for IHC quantitation depends both on the performance of the IHC IA, and the ability to manually read digital IHC slides on the monitor. A multisite study was conducted to compare the manual reading of IHC Human Epidermal Growth Factor Receptor 2 (HER2) slides on a monitor, using Aperio Technologies, Inc. ScanScope XT instrument and the Spectrum digital pathology information management system to conventional manual microscopy (MM).

Design: A total of 180 breast cancers were immunohistochemically stained using Dako HercepTest and assayed: (site 1) 80 retrospective specimens with equal HER2 score distribution from an academic center, and (site 2) 100 prospective specimens from a reference laboratory. At each site, 3 pathologists carried out a blinded read of the glass slides using a conventional light microscope, and reporting the HER2 score for each. The glass slides were scanned using a 20× objective, and after a wash-out period and randomization of the slides, the same 3 pathologists carried out another blinded read of the same slides, but this time of the digital image of the slides on the monitor, again reporting the HER2 score. Each of the methods: MM and reading digital slides on a computer monitor, from now on called manual digital read (MDR) were evaluated separately and comparatively using Percent Agreement (PA) of negative HER2 scores (0, 1+) versus equivocal (2+) versus positive HER2 scores (3+).

Results: Comparable PA values were obtained for MM and MDR IHC HER2 images on the monitor (MM: 76.3% to 91.3%; MDR: 70.0% to 86.0%; MM vs. MDR: 61.3% to 92.5%).

Conclusions: Results of manually reading IHC HER2 slides on a monitor using Aperio Technologies, Inc. digital pathology system show substantial equivalence to those obtained by conventional manual microscopy. The digital slides are easily read on a monitor.