A quality assurance exercise to evaluate the accuracy and reproducibility of chromogenic in situ hybridisation for HER2 analysis in breast cancer.

BACKGROUND: Chromogenic in situ hybridisation (CISH) is an alternative to immunohistochemistry or FISH for the assessment of HER2 oncogene status in breast cancer. Although CISH is being used increasingly in routine diagnostics, there are no established inter-laboratory quality assurance programmes for this test. METHODS: The reproducibility of HER2 CISH analysis was assessed when performed by seven different centres that use the test routinely in diagnostic service. RESULTS: The results from 28 cases showed overall concordance of 98.5% (192/195 tests; kappa coefficient 0.91). One of the discrepancies was due to the invasive carcinoma having been cut out in the sections received by two of the centres, and the other two were in the non-amplified/equivocal/low-amplified category. CONCLUSION: This is believed to be the first report of a quality assurance study assessing laboratories that use HER2 CISH routinely in clinical diagnostics. The results show that CISH is a robust technique providing a suitable assay for the frontline testing of HER2 status in breast cancer.