Chromogenic in situ hybridisation testing for HER2 gene amplification in breast cancer produces highly reproducible results concordant with fluorescence in situ hybridisation and immunohistochemistry.
OBJECTIVE
The objective of this study was to evaluate the accuracy, ease of use and reproducibility of chromogenic in situ hybridisation (CISH) for HER2 testing by studying its inter-laboratory concordance in five Australian pathology laboratories.


METHODS
The HER2 status of 49 breast cancers was determined by CISH twice in two different laboratories. Each sample had previously been tested by immunohistochemistry (IHC; 2+ and 3+ cases selected) and fluorescence in situ hybridisation (FISH). Participating laboratories were blinded to these test results. Oestrogen receptor (ER) status was also evaluated for each cancer.


RESULTS
High correlation was observed between FISH and CISH results. No cases showing high gene amplification by FISH were scored as non-amplified by CISH (kappa coefficient = 1). High correlation was observed between IHC and CISH, all IHC 3+ samples showing amplification by CISH. Inter-laboratory CISH concordance was also good (kappa coefficient = 0.67). Fifty-six per cent of HER2-amplified samples tested ER positive, while 42% of ER-positive cases showed HER2 gene amplification, confirming that HER2 testing should not be confined to ER-negative breast cancers.


CONCLUSIONS
These findings demonstrate that CISH is a robust test to assess HER2 status in breast cancer and therefore is an important addition to the HER2 testing algorithm.
Westmead Hospital, Sydney, NSW, Australia. Michaelb@icpmr.wsahs.nsw.gov.au
Michael
M
Bilous
Adrienne
A
Morey
Jane
J
Armes
Margaret
M
Cummings
Glenn
G
Francis
D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D002863:Chromogenic Compounds; D005260:Female; D005784:Gene Amplification; D018734:Genes, erbB-2 / Q000235:genetics*; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods*; D017404:In Situ Hybridization, Fluorescence; D015203:Reproducibility of Results
D002863:Chromogenic Compounds