Introduction: Currently laboratory methods for HER2 assessment include immunohistochemical (IHC) methods (measuring protein overexpression) and fluorescence in situ hybridization (FISH) (measuring gene amplification). The measure of HER2 protein by IHC is usually assessed by the mouse monoclonal antibody CB11, and polyclonal antibodies (Herceptest) directed against the internal portion of the receptor. Recently, chromogenic in situ hybridization (CISH), in which HER2 is detected by a peroxidase reaction and the gene amplification can be determined by regular bright-field microscopy, has emerged as an alternative to FISH.
Aims: The aim of this study was to evaluate the status of HER2 in tissue microarrays (TMAs) of invasive breast cancer using the novel rabbit monoclonal antibody SP3 directed against the external portion of HER2 and correlate the results with CB11 and CISH.
Methods: We performed IHC with two antobodies (CB11 and SP3) and CISH for HER2 in 10 TMA blocks with 190 formalin-fixed paraffin-embedded cases of invasive breast carcinomas.
Results: The correlation between SP3 and CB11 was statistically significant (p<0.0001) with an agreement rate of 86.9%. When we compare the staining pattern of the two antibodies, we observe that the majority of SP3 immunostainings were easier assessed, with a strong complete membrane staining pattern without non-specific cytoplasmic staining. We observed also a good correlation between SP3 and CISH (p<0.0001). Twenty-three among 24 SP3 +++ cases showed gene amplification, 97.3% of the cases without gene amplification were SP3 negative and six of the seven cases SP3 2+ were amplified.
Conclusion: The high level of agreement between SP3, a monoclonal antibody that recognizes the extracellular domain of the HER2 receptor, and CB11 and CISH, demonstrates that this novel antibody is a reliable candidate to evaluate the expression of HER2 in breast cancer cases.
- breast cancer