ORIGINAL ARTICLE

HER2 evaluation using the novel rabbit monoclonal antibody SP3 and CISH in tissue microarrays of invasive breast carcinomas

Sara Alexandra Vinhas Ricardo¹, Fernanda Milanezi¹, Sílvia Teresa Carvalho¹, Dina Raquel Aguilera Leitão² and Fernando Carlos Lander Schmitt^1,2

¹ IPATIMUP, Institute of Molecular Pathology and Immunology, University of Porto, Porto, Portugal
² Medical Faculty of Porto University, Porto, Portugal

Correspondence to:
Correspondence to:
Professor Fernando Schmitt
Rua Roberto Frias s/n, 4200 Porto, Portugal; fschmitt{at}ipatimup.pt

Background: Laboratory methods for HER2 assessment currently include immunohistochemical (IHC) methods (measuring protein overexpression) and fluorescence in situ hybridisation (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 hybridisation (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: 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: IHC was performed with two antibodies (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 significant (p<0.001) with an agreement rate of 86.9%. When the staining pattern of the two antibodies was compared, the majority of SP3 immunostainings were assessed more easily, with a strong complete membrane staining pattern without non-specific cytoplasmic staining. There was a good correlation between SP3 and CISH (p<0.001). 23/24 SP3 3+ cases showed gene amplification, 97.3% of the cases without gene amplification were SP3 negative, and 6/7 SP3 2+ were amplified.

Conclusion: The high level of agreement between SP3, a monoclonal antibody that recognises the extracellular domain of the HER2 receptor, and CB11 and CISH, shows that this novel antibody is a reliable candidate to evaluate the expression of HER2 in breast cancer.

Abbreviations: CISH, chromogenic in situ hybridisation; FISH, fluorescence in situ hybridisation; IHC, immunohistochemistry; TMA, tissue microarray

Keywords: HER2; CISH; SP3; TMA; breast cancer

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