Abstract P2-04-10: Utility of simultaneous HER2 protein and gene assessment for the evaluation of discrepancy and intratumoral heterogeneity of HER2 status and the prediction of prognosis in invasive breast cancer using the gene-protein assay (GPA)

1036 Background: Intratumoral heterogeneity (ITH) occurs as a consequence of epigenetic aberrations in tumor cells with genetic diversity. HER2 ITH can be classified into genetic (a mixture of tumor cells with and without HER2 gene amplification) and epigenetic ITH (a mixture of HER2 gene-amplified tumor cells with and without HER2 protein overexpression). However, the both effects of genetic and epigenetic ITH on HER2-targeted therapy have not been clearly demonstrated. In order to implement ITH as a referenced factor for treatment selection, the ITH quantification is necessary. Gene-protein assay (GPA), in which immunohistochemistry and dual in situ hybridization are simultaneously performed on a single slide, allows bright-field analyses of both gene and protein status. We aimed to quantify HER2 ITH by the combination of gene and protein status and clarify its clinical significance. Methods: Fifty three patients with HER2-positive breast cancer, who underwent neoadjuvant trastuzumab with chemotherapy, were examined. Five representative microscopic images were captured from a GPA slide of a pre-therapeutic biopsy material. All evaluable tumor cells in the images were scored according to the HER2 status determined by the combination of gene copy number and protein expression (Table). We investigated the relationship between the HER2 scores and pathological complete response (pCR) to the neoadjuvant treatment by the logistic analysis. Results: The average of HER2 scores, indicating the degree of the HER2 status, varied from 2.21 to 5.98. It was significantly related to pCR (Estimate: 1.21, Std. error: 0.46, RR: 3.34, P=0.009, 95%CI: 1.35-8.25). The standard deviation of HER2 scores, indicating the degree of the HER2 ITH, varied from 0.13 to 1.37. It was significantly related to pCR (Estimate: -2.09, Std. error: 0.83, RR: 0.12, P=0.012, 95%CI: 0.02-0.63). Conclusions: HER2 ITH, quantified by GPA, is a predictive factor for the therapeutic effect to trastuzumab-based treatment in HER2-positive breast cancer. [Table: see text]

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HER2 Testing in Invasive Breast Cancer: A Comparison Between Immunohistochemistry and Fluorescence In Situ Hybridization Assays

Research in Molecular Medicine ◽

10.32598/rmm.8.3.1133.1 ◽

2020 ◽

Vol 8 (3) ◽

pp. 139-146

Author(s):

Maryam Moradi Chaleshtori ◽

◽

Zohreh Hojati ◽

Ali Jazaeri ◽

Hossein Teimori ◽

...

Keyword(s):

Breast Cancer ◽

In Situ Hybridization ◽

Fluorescence In Situ Hybridization ◽

Gene Amplification ◽

Invasive Breast Cancer ◽

Concordance Rate ◽

Her2 Status ◽

Her2 Gene ◽

Relative Copy Number

Background: HER2 status testing in breast cancer is crucial for the detection of eligible patients for trastuzumab therapy. In this study, the relative copy number of HER2 gene, in patients with breast cancer, was determined by fluorescence in situ hybridization (FISH) and the results were compared with those of immunohistochemistry (IHC) to obtain the concordance rate between these two methods. Material and Methods: HER2 status of 31 invasive breast cancer samples was compared using IHC and FISH techniques. The ratio of HER2/CEP17 was used to determine the amplification of the HER2 gene. If the ratio of HER2/CEP17 is greater than 2.2, HER2 gene amplification has occurred in the cancer cells. Then, a comparative analysis is performed to estimate the concordance rate between FISH and IHC results. Results: The gene amplification of HER2 was observed in 26% of cases by FISH. The IHC and FISH results showed 100%, 36.36%, and 85.71% concordance rates for cases with IHC scores of 3+, 2+, and 0/+1, respectively. The overall concordance between the two methods was 80%. Based on statistical analysis, HER2 status showed a considerable correlation with tumor grade (P= 0.02). No correlation was observed between HER2 gene status and the size and type of tumor, characteristics of lymph node, and patients’ age. Conclusion: The data suggested that IHC results are reliable for HER2 status testing in cases with IHC scores 0/+1 and 3+. However, in patients with an IHC score of +2, it is necessary to perform a complimentary test to evaluate HER2 status to avoid haphazard treatment with trastuzumab in negative cases and identifying positive cases for suitable treatment.

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