HER2 diagnostics in gastric cancer—guideline validation and development of standardized immunohistochemical testing

Abstract

Trastuzumab-based therapy has been shown to confer overall survival benefit in HER2-positive patients with advanced gastric cancer in a large multicentric trial (ToGA study). Subgroup analysis identified adenocarcinomas of the stomach and gastroesophageal (GE) junction with overexpression of HER2 according to immunohistochemistry (IHC) as potential responders. Due to recent approval of trastuzumab for HER2 positive metastatic gastric and GE-junction cancer in Europe (EMEA) HER2 diagnostics is now mandatory with IHC being the primary test followed by fluorescence in situ hybridization (FISH) in IHC2+ cases. However, in order to not miss patients potentially responding to targeted therapy determination of a HER2-positive status for gastric cancer required modification of scoring as had been proposed in a pre-ToGA study. To validate this new HER2 status testing procedure in terms of inter-laboratory and inter-observer consensus for IHC scoring a series of 547 gastric cancer tissue samples on a tissue microarray (TMA) was used. In the first step, 30 representative cores were used to identify specific IHC HER2 scoring issues among eight French and German laboratories, while in the second step the full set of 547 cores was used to determine IHC HER2 intensity and area score concordance between six German pathologists. Specific issues relating to discordance were identified and recommendations formulated which proved to be effective to reliably determine HER2 status in a prospective test series of 447 diagnostic gastric cancer specimens.

Assessment of ErbB2 (Her2) in oesophageal adenocarcinomas: summary of a revised immunohistochemical evaluation system, bright field double in situ hybridisation and fluorescence in situ hybridisation

“…3,8,10 For immunohistochemistry, we used the 4B5 assay. This antibody has also been approved by the FDA for ErbB2 testing in breast cancer and appeared to be at least as sensitive and may even show a higher inter-laboratory concordance for ErbB2 scoring and a closer relationship between immunohistochemi- ErbB2 positivity is defined as immunohistochemistry 3+ and/or an ErbB2/Chr17 quotient of X2 as assessed by in situ hybridisation.…”

“…10 There is the evidence that the determination of ErbB2 status by transferring the breast cancer immunohistochemistry scoring roles to gastric cancer may lead to a significant number of falsenegative ErbB2 tumours. 20 Comparison between studies that have assessed ErbB2 in gastric cancer using the breast cancer evaluation system, on the one hand, and those that used the modified scoring system for gastric cancer, on the other hand, reveals significantly higher ErbB2 rates after the application of the proposed gastric cancer scoring system.…”

“…The method of ErbB2 scoring was essentially based on previously described recommendations, which was also applied in the ToGA study for gastric cancer and is described in detail elsewhere. 3,10 Briefly, the major features of the modification that are different from the ErbB2 scoring in breast cancer are as follows: a positive reaction is considered a membranous staining pattern that can be unequivocally assessed as linear staining at cell-cell contact sites and includes baso-lateral or lateral without restriction on the circularity of staining; the degree of microscopic magnification (x-fold) at which the membranous (linear intercellular) staining is clearly visible for the estimation of ErbB2 staining intensity is considered; the 10% minimum number of stained tumour cells that could reliably be assessed for ErbB2 staining in biopsies is eliminated. In this study, at least five cohesive, unequivocally stained evaluable cells are considered to be the limit for ErbB2 evaluation ( Figure 1).…”

“…Therefore, for gastric cancer, a modified ErbB2 scoring system for immunohistochemistry has been proposed. 3,10 Data on ErbB2 in oesophageal adenocarcinomas exist to a lesser extent than gastric cancer. The rate of ErbB2 overexpression/amplification in these cancers has been reported at approximately 20-25%, depending on the method of evaluation and the definition used.…”

“…For this purpose, we applied the revised ErbB2 immunohistochemistry scoring recommendations for gastric cancer 3,10 to a tissue microarray that comprised a large number of primary resected oesophageal adenocarcinomas. In addition, in situ hybridisation was performed using the recently developed bright field double in situ hybridisation.…”