OBJECTIVEThrough comparison of HER2/neu oncogene detected by chromogenic in situ hybridization (CISH) and immunohistochemistry (IHC) in breast cancer, to explore the effect of CISH on detecting gene amplification of HER2.

METHODSSelected formalin-fixed paraffin-embedded breast samples whose pathological types were infiltrating ductal carcinomas (255 retrospective samples, 271 prospective samples), and these samples were detected by IHC and CISH.

RESULTS(1) In the retrospective study, CISH identified gene amplification in 91.6% of IHC score 3+ tumors (120/131) and in 56.5% of IHC score 2+ tumors (39/69), thus the concordant ratio between IHC and CISH was 81.2% (207/255). The two results showed significant correlation (P<0.01). (2) In the prospective study, the ratio of HER2 protein over expression detected by IHC was 31.7%, the ratio of HER2 gene amplification detected by CISH was 27.3%. CISH identified gene amplification in 91.4% of IHC score 3+ tumors (53/58) and in 46.4% of IHC score 2+ tumors (13/28), Concordant ratio between IHC and CISH was 89.7% (243/271). Two results showed significant correlation (P<0.01). (3) Paired CISH/FISH results were concordant in 14 of 15 cases. The remaining case was detected by FISH, but showed no HER2 gene amplification by CISH. (4) The gene amplification by CISH had a significantly reverse correlation with ER and PR expression (P<0.01).

CONCLUSIONSThe results of HER2 gene amplification detected by CISH have high concordance with the results detectd by IHC and FISH. CISH is a novel technique for detecting HER2 gene amplification.