A novel gene–protein assay for evaluating HER2 status in gastric cancer: simultaneous analyses of HER2 protein overexpression and gene amplification reveal intratumoral heterogeneity

Abstract

Background Human epidermal growth factor receptor 2 (HER2) protein overexpression and gene amplification are important biomarkers for trastuzumab treatment in breast and gastric cancer patients. Gastric cancer presents high rates of tumor heterogeneity, which may influence the results of HER2 testing. A novel gene-protein assay (GPA) can allow the simultaneous analysis of HER2 protein and gene status on a single slide.Methods Using the tissue microarray technique, the HER2 status of each of 875 gastric cancer cases was evaluated by immunohistochemistry (IHC), brightfield dual-color in situ hybridization (DISH), and GPA. Intratumoral phenotypic and genotypic heterogeneity were evaluated by comparing the HER2 statuses of two tissue cores from each case. Results There was excellent concordance between GPA and IHC (99.2 %), as well as between GPA and DISH results (99.3 %). HER2 positivity obtained by GPA was almost identical (99.8 %) to the results obtained by IHC and DISH assays. Intratumoral phenotypic heterogeneity was more frequently observed in IHC 2? cases (63.5 %) compared with IHC 3? cases (28.3 %). Phenotypic heterogeneity (48.8 %) was more frequently observed than genotypic heterogeneity (26.8 %). Tumor heterogeneity was consistently observed from early to advanced stages. Conclusions HER2-positive gastric cancers presented different levels of HER2 protein expression and gene amplification statuses within the same lesion in almost half the cases examined. Evaluating both phenotypic and genotypic heterogeneity may contribute to a deeper understanding and improved prediction of clinical outcome in gastric cancer patients treated with trastuzumab. This newly established GPA technology may also be useful for developing biomarkers for other molecularly targeted therapies.

Digital Image Analysis of HER2 Immunostained Gastric and Gastroesophageal Junction Adenocarcinomas

“…The assay allows simultaneous interpretation of HER2 protein expression and HER2 gene amplification in the same slide. Few studies have evaluated the assay for GGEJ adenocarcinomas, exhibiting promising results 27–29…”

Loss of Heterozygosity of PTEN (Encoding Phosphate and Tensin Homolog) Associated with Elevated HER2 Expression Is an Adverse Prognostic Indicator in Gastric Cancer

“…On the basis of the biological difference, it has been pointed out that HER2 protein expression and gene amplification is heterogeneous in gastric cancer compared with breast cancer. Previous reports noted that the HER2-equivocal staining group showed more phenotypic heterogeneity than the HER2-positive staining group [24], and almost 50% showed gene amplification. On the basis of this information, we decided to include the HER2-equivocal group in the HER2-positive group and defined them as HER2-expressing gastric cancer.…”

Monitoring the HER2 copy number status in circulating tumor DNA by droplet digital PCR in patients with gastric cancer

“…Furthermore, the number of patients eligible for trastuzumab treatments is limited. Because the distribution of HER2-expressing cells is known to be heterogeneous in GC [4], HER-2 positivity in resected tumors may provide insufficient information for determining eligibility for trastuzumab treatments because of the temporal and spatial intratumoral and intertumoral heterogeneities of this disease. Recurrent tumors from HER2-positive cases may contain HER2-negative tumor cells as a major population, whereas HER2 amplification/overexpression may be acquired or HER2-positive cells existing as a minor population in resected tumors may be selected during treatment progress in HER2-negative cases.…”