HER2 Status: What is the Difference Between Breast and Gastric Cancer?

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1 Ask the Experts HER2 Status: What is the Difference Between Breast and Gastric Cancer? Bharat Jasani MBChB, PhD, FRCPath Marco Novelli MBChB, PhD, FRCPath Josef Rüschoff, MD Robert Y. Osamura, MD, FIAC Professor/Head of Pathology Department of Medical Genetics, Haematology & Pathology, Cardiff University School of Medicine UHW Main Building Heath Park, Cardiff, UK CF14 4XN Professor of Gastrointestinal Pathology, Department of Histopathology Rockefeller Building University Street London, UK WC1E 6JJ Professor for Pathology CMO Targos Molecular Pathology GmbH Germaniastr. 7. D Kassel, Germany Professor of Pathology Tokai University School of Medicine Tokyo, Japan What are the Key Differences Between HER2 Expression in Breast and Gastric Cancer? Gastric cancer is the second largest cause of cancer associated death world-wide. Surgery remains the mainstay of treatment for the resectable cancer. However with the noted high frequency of locoregional and distant recurrences and relatively low 5-year survival for symptomatic Stage II-III and Stage IV cancer (20-50% and 5-10%, respectively), there has been a need to develop more effective peri-operative and adjuvant therapies for Stage II-IV disease (1) and in some countries with a high incidence of gastric cancer (such as Japan) screening programs have been established for the detection of Stage I resectable disease which has a 90% chance of 5-year survival (1). More recently several novel approaches based on molecular targeting have also been attempted including the use of anti-vegf (2), EGFR (3) or HER2 (4) monoclonal antibodies combined with chemotherapy. Of these the comparative use of trastuzumab (anti-her2) in combination with 5FU, or capecitabine and cisplatin versus chemotherapy alone in a Phase III Trial (ToGA Trial) on HER2-positive advanced (i.e., locally advanced or metastatic) gastric cancer patients, has shown significantly improved median survival (13.8 vs months; p<0.0046; HR 074; 95% CI ) (4). Meta-analysis has shown HER2 over-expression rate of 15-40% in gastric cancer with a putative association with poor prognosis (5). These findings taken together have provided a rationale for routine HER2 testing of advanced gastric cancer as the basis for selecting patients for adjuvant anti-her2 treatment. As observed with breast cancer, there is however, the need from the outset to avoid unnecessary treatment, the risk of side effects and high cost of the anti-her2 therapy through use of accurate and reproducible methods for determination of the HER2 status of gastric The overall reliability of HER2 testing in breast cancer has been shown to be affected by a multiplicity of preanalytical, analytical and post-analytical variables. cancer (6, 7). The overall reliability of HER2 testing in breast cancer has been shown to be affected by a multiplicity of pre-analytical, analytical and post-analytical variables. The principal aim of this presentation is to highlight these differences as a precaution to routine HER2 testing of gastric cancer based on principles established for breast cancer. 58 Connection 2010

2 Key Differnces: HER2 Expression in Breast Cancer vs. Gastric Cancer Feature Breast Cancer Gastric Cancer Character of HER2 Associated Membrane Staining and the Frequency of its Association with HER2 Gene Amplification Intensity of HER2 IHC Staining vs. (Frequency of gene amplification) Membranous cellular distribution Extent of HER2 staining in a HER2 3+ case Strong (+++) (95-98%) Moderate (++) (~20%) Weak (+) (~2%) Predominantly Circumferential Frequently diffuse or at least >30% Incidence of Tumor Heterogeneity Apparent sub-clonal diversity in gene Rare amplification Requirements for Verification of Gene Amplification Status Preferred method Fluorescence In Situ Hybridization (FISH) Recommended method of tumor cell sampling Random selection of 20 invasive cancer cells Strong (++ +; Fig. 1a & 2b) (95-100%) Moderate (++; Fig. 1b & 4a) (~50%) Weak (+; Fig. 1c & 4b) (~7.5-25% see Reference 3 and 4) Predominantly Basolateral ( U -shaped) or lateral (parallel lines) (cf. Fig. 1a) Frequently Focal with >10% sufficient for resection specimens and 5-20 contiguous of HER2-positive tumor cells sufficient for small biopsy specimens (cf. Fig. 4) Frequent (cf. Fig. 3 & 4) Brightfield Dual In Situ hybridization (BDISH) (cf. Fig. 2 & 4) Targeted selection of IHC 2+ positive malignant cells (cf. Fig. 4) Relationship with Tumor Progression Status In situ (breast) In situ/dysplasia (gastric) Inconsistent Uncertain due to increased heterogeneity associated with more advanced stages of tumour progression Primary vs. metastatic Consistent Most probably consistent Relationship with Tumor Subtypes Glandular Frequent involvement of ductal type Frequent involvement of intestinal type adenocarcinoma (cf. Fig. 3 & 5) Diffuse Infrequent involvement of lobular type Variation of Incidence with Anatomic Location Generally absent Relationship with Poor Prognosis Consistent Predictive Value of HER2 IHC- or HER2 ISH+ Status HER2 IHC+/HER2 ISH+ tumor status has equal predictive value to HER2 IHC-/HER2 ISH+ status Infrequent involvement of diffuse signet ring subtype (cf. Fig. 3 & 5) Most frequent proximal stomach including the oesophageal-gastric junction (OGJ) Least frequent towards distal stomach Inconsistent HER2 IHC+ and HER2 ISH+ tumor status has greater predictive value value compared to HER2 IHC-/HER2 ISH+ tumor status (see Reference 3 and 4) Connection

3 3+ 2+ Figure 1a. Readily visible with a 4x objective. Figure 1b. Readily visible with a 20x objective. 1+ Figure 1a-c. Objective lens directed intensity related grading of HER2 IHC staining in gastric cancer. Figure 1c. Readily visible with a 40x objective. 60 Connection 2010

4 Figure 2. (a) Uniform HER2 gene amplification associated with (b) the area of strong intensity HER2 IHC staining in gastric cancer as shown in Figure 1. Figure 2a. 3+ Figure 2b. Connection

5 Figure 3. Focal/Heterogeneous bi-clonal/tumor type associated HER2 IHC expression & gene amplification in gastric cancer. Tumor Heterogeneity Cohesive IHC 3+ and FISH+ ve clone Signet ring type Intestinal gland forming type 62 Connection 2010

6 2+ 1+ Figure 4a. Figure 4b. Figure 4a-c. Focal/Heterogeneous sub-clonal/intra-tumoral variation in HER2 IHC expression (a, b) and gene amplification (c) in gastric cancer. Biopsy: Score 3+. Focal staining (<10%) membranous staining. + Clearly visible with a 2.5x objective (3+) Only visible with a 10x objective (2+ equivalent) Figure 4c. Connection

7 Common location of intestinal metaplasia & oesophageal gastric junction type adenocarcinoma with evidently the most frequent (~33%) association with clinically significant HER2 IHC expression/gene amplification Common location of intestinal type gastric adenocarcinoma with frequent association with clinically significant HER2 IHC expression/gene amplification Common location of diffuse signet ring type gastric adenocarcinoma with least frequent (~5%) association with clinically significant HER2 IHC expression/gene amplification 5 1. Esophagus 2. Cardia 3. Fundus 4. Body 5. Pylorus 6. Pyloric canal 7. Pyloric sphincter 8. Duodenum Figure 5. Prevalence of HER2 expression in association with anatomic location/type of gastric adenocarcinoma. Glossary Glandular type tumor: i.e., Intestinal type Gastric Adenocarcinoma or ductal type breast carcinoma. Diffuse type tumor: Diffuse signet ring type Gastric Adenocarcinoma or lobular type breast carcinoma. Sub-clonal diversity: Variation in HER2 status (IHC and/or ISH based) due to genetic changes affecting the single parental clone giving rise to the primary tumor. Multi-clonal diversity: Variation in HER2 status (IHC and/ or ISH based) due to genetic changes affecting separate parental clones giving rise to the primary tumor. References 1. Foukakis T, et al. Advances in the treatment of patients with gastric adenocarcinoma. Acta Oncol 2007; 46: Shah, et al. Multicenter Phase II Study of Irinotecan, Cisplatin, and Bevacizumab in Patients With Metastatic Gastric or Gastroesophageal Junction Adenocarcinoma. J Clin Oncol 2006; 24: Meza-Junco, et al. Trastuzumab for gastric cancer. Expert Opin Biol Ther 2009; 9: Bang Y-I, et al. Trastuzumab in combination with chemotherapy versus chemotherapy alone for treatment of HER2-positive advanced gastric or gastro-oesophageal junction cancer (ToGA): a phase 3, open-label, randomised controlled trial. The Lancet 2010; Gravalos C and Jimeno A. HER2 in gastric cancer: a new prognostic factor and a novel therapeutic target. Annals of Oncology 2008; 19: Hofmann M, et al. Assessment of a HER2 scoring system for gastric cancer: results from a validation study. Histopathology 2008; Rüschoff J, et al. HER2 diagnostics in gastric cancer guideline validation and development of standardized immunohistochemical testing Virchows Arch 2010; 457: Connection 2010