It really looks like IHC testing should remain in the purview of central reference laboratories. One of the reasons may be that a number of the large reference laboratories are now using digital image analysis for all of their IHC scoring. Digital image analysis takes some of the guesswork out of the interpretation of these IHC assays. There can be honest disagreement between good pathologists over the difference between a 2+ and a 3+, but a computer can actually read the same slide over and over again and give you the exact same result.

Pathologists actually call up the information on a digital screen to confirm and double check the assay performance. In most of the large studies in which head-to-head comparisons have been done with digital image analysis and FISH for HER2 testing, the concordance rate is about of 90 percent.

The remarkable feature of this type of assay is you can take a slide, score it using the digital assay system, and then read it a hundred years later and get the same answer. It’s really highly reproducible in terms of run-to-run variability, much more than the manual read-out for IHC. Even if you give a good pathologist a test set of slides to read and ask them to re-read the same set some time later, there will be some variability that you can’t control. This instrument removes that type of variability.

Mark Pegram, MD