OBJECTIVETo determine human epidermal growth factor receptor 2 (HER2) status in breast carcinoma by the techniques of a fully automated immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH), to compare the concordance of protein expression with gene amplification and to explore the optimization in process quality control.

METHODSA prospective study of invasive breast cancer specimens excised between May 2009 and April 2011 at the Cancer Hospital, Chinese Academy of Medical Sciences was conducted by automated IHC staining with the new 4B5 rabbit monoclonal antibody and FISH. An evaluation was performed according to the ASCO/CAP guidelines (2007) and Chinese guidelines (2009). The gene amplification status of 740 cases were detected by FISH.

RESULTSA total of 2420 cases of breast invasive ductal carcinoma without pre-operation therapy were tested by automated IHC. 551 cases (22.8%) were scored as positive (3+), 664 cases (27.4%) as equivocal (2+), and 1205 cases (49.8%) as negative (1+/0). Gene amplification was detected in 98.0% (242/247) HER2 protein expression positive (3+) cases and in 13.6% (53/389) equivocal (2+) cases. One of 247 (0.4%) HER2 expression 3+ cases and 5 of 389 (1.3%) HER2 expression 2+ cases were equivocal for gene amplification. No gene amplification was detected in expression negative (1+/0) cases by FISH (0/104). The overall concordance between IHC and FISH was 98.6% [(242 + 104)/(247 + 104)].

CONCLUSIONSThere is a high concordance rate between automated IHC with 4B5 rabbit monoclonal antibody and FISH results for assessing the HER2 gene amplification status in surgically-excised breast cancer specimens, suggesting that automated IHC with 4B5 antibody can provide a reliable method to detect HER2 overexpression for eligibility of HER2 targeted therapy.