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HER2 testing in gastric cancer – a practical approach

HER2 testing in gastric cancer – a practical approach. Recommendation publication by J. Rüschoff et al. Modern Pathology 2012. HER2 testing in Gastric Cancer Recommendations.

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HER2 testing in gastric cancer – a practical approach

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  1. HER2 testing in gastric cancer – a practical approach Recommendation publication by J. Rüschoff et al. Modern Pathology 2012

  2. HER2 testing in Gastric Cancer Recommendations The HER2 testing in Gastric Cancer recommendationshavebeendevelopedbyan international expert panel with extensive HER2 testing experience in breast and gastric cancer, based on the trastuzumab Gastric cancer study Topics covered in thepublication: • Introduction of the HER2 testing and objections of the publication • Epidemiology of gastric cancer • HER2 as a therapeutic target in general and specifically in gastric cancer • Comparison of HER2 testing in gastric cancer and breast cancer • Practical guidance on HER2 testing in gastric cancer: covering all steps from sample collection, preparation, sample scoring, up to quality assurance.

  3. Key Messages of the Recommendation publication on HER2 Testing In Gastric Cancer Accurate patient identification is possible if guidelines are adhered to IHC is the initial testing modality in gastric cancer ISH should be used to re-test IHC2+ cases (or for difficult cases) Bright-field methods should be preferred over dark-field methods for ISH testing Specific training is required for GC testing irrespective of any prior BC experience

  4. Gastric Cancer HER2 Testing: Main recommendations in brief • All patients with gastric cancer should be tested for HER2 status at the time of initial diagnosis • Scoring should be performed in adherence to the recommendations specifically devised for GC • The use of validated IHC and ISH tests is strongly recommended • Laboratories should participate in validated quality assurance programs

  5. HER2 Testing in Gastric Cancer: Key Recommendation Summary for IHC and ISH • immunohistochemistry (IHC) • Representative surgical samples or an adequate number of viable biopsy specimens (ideally 6–8) are required • If few biopsies are available, all viable specimens should be tested • IHC should be the initial HER2 testing methodology for gastric cancer and bright-field methodologies are preferred wherever possible • HER2-positive per EMA license: IHC 3+ or IHC 2+/FISH-positive or IHC 2+/SISH-positive • Borderline IHC 1+/IHC 2+ cases and samples with focal and intense membranous reactivity in <10% cells may also be retested with FISH or SISH (scores for both assays should be indicated separately on the report) • Validated IHC HER2 assays should be used • Scoring recommendations • Due to the tumor heterogeneity (focal areas of positivity) and incomplete membrane staining commonly seen in gastric cancer, the gastric cancer-specific scoring criteria should be adhered to: • Surgical specimen cutoff: complete, basolateral, or lateral membranous reactivity in ≥10% of cells • Biopsy specimen cut-off: complete, basolateral, or lateral membranous reactivity in 5 clustered cells • The ‘magnification rule’ should be used in conjunction with the scoring criteria • Borderline cases (IHC 1+/IHC 2+ or focal staining in <10% cells) that score FISH-positive or SISH-positive may be considered HER2-positive (scores for both assays should be indicated separately on the report) • in situ hybridisation(ISH) • Tumor samples classified as IHC 2+ should be retested by FISH or SISH to assess HER2 status • SISH is a more suitable methodology than FISH for assessing HER2 status in gastric tumor samples as it is a bright-field methodology and thus allows for rapid identification of HER2-positive tumor foci within a heterogeneous sample • Validated ISH HER2 assays should be used • Scoring recommendations • The definition of FISH or SISH positivity in gastric or GE junction cancer is a HER2:CEP17 ratio of ≥2.0 • The entire case should be screened for amplified regions (particularly important for FISH samples where a bright-field image is not available) • At least 20 evaluable, non-overlapping cells in the invasive component should be counted initially • In borderline amplification cases, approximately 20 additional cells should be recounted or scoring should be performed in an alternative area of tissue • The overall HER2 gene count is important: • o >6 HER2 gene copies using single probe: considered positive • o 4–6 HER2 gene copies: dual probe test advised and the ratio should be recalculated by counting an additional 20 cells • Ensuring quality and timely HER2 testing results • The use of validated IHC and ISH tests is strongly recommended and appropriate controls should be included in each run • Turnaround time from initial diagnosis to reporting of results should ideally not exceed 5 working days and a multidisciplinary approach is required • Centralized testing is recommended wherever possible and all laboratories should participate in validated QA programs

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