SUMMARY: It is estimated that in 2016 GastroEsophageal Adenocarcinoma (GEA) accounted for 43,280 new cases in the United States. Majority of the patients with GEA have advanced disease at the time of initial presentation and have limited therapeutic options with little or no chance for cure. Patients with localized disease (stage II and stage III) are often treated with multimodality therapy and 40% of the patients may survive for 5 years or more. Approximately 7-38% of GEAs have amplification and/or overexpression of HER2. HER2 (ERBB2) is a proto-oncogene located on the long arm of chromosome 17 (17q12) that encodes a tyrosine kinase receptor, which upon dimerization and phosphorylation, initiates signaling pathways, that lead to cell division, proliferation, differentiation and anti-apoptosis signaling.
GastroEsophageal junction tumors have a higher incidence of overexpression of HER2 compared to gastric cancers. In the stomach, overexpression of HER2 varies with histologic type (intestinal-type having greater expression than diffuse-type) and differentiation (well and moderately differentiated tumors having greater expression than poorly differentiated tumors). Further, the heterogeneity of immunostaining is greater in GEA and the complete membrane staining required for positivity in breast cancer, is not common in GEA. Due to the high heterogeneity of a gastric cancer, it is appropriate to evaluate HER2 expression on biopsy specimens, especially in unresectable cases and reevaluate it on resected specimens, when available.
The NCCN (National Comprehensive Cancer Network) Clinical Practice Guidelines in Oncology for Gastric Cancer and Esophageal and Esophagogastric Junction Cancers, recommend assessment of HER2 overexpression using ImmunoHistoChemistry and/or gene amplification using FISH (Fluorescence In Situ Hybridization or another in situ hybridization method, in tumor samples from patients, with unresectable, locally advanced, recurrent, or metastatic GEA, for whom HERCEPTIN® may be potentially beneficial. Testing for HER2 is primarily performed on Formalin-Fixed and Paraffin-Embedded biopsy or resection tumor tissue from the primary or metastatic site. There are important differences in HER2 expression, scoring, and outcomes in GEA compared to breast carcinoma, and the need for HER2 guidelines (that include critical clinical and laboratory considerations) was therefore recognized. The CAP, American Society for Clinical Pathology, and ASCO convened an international expert panel to systematically review published documents and to develop an evidence-based guideline, to establish recommendations for HER2 testing in GastroEsophageal Adenocarcinoma.
HERCEPTIN® (Trastuzumab) is humanized monoclonal antibody that targets HER2. HERCEPTIN® is effective only in cancers where HER2 is overexpressed. In a previously published randomized phase III trial, HERCEPTIN® in combination with chemotherapy was shown to significantly improve Overall Survival compared with chemotherapy alone, in patients with HER2 positive advanced GEA.
The following are the Guideline Summary from the College of American Pathologists, American Society for Clinical Pathology, and American Society of Clinical Oncology
• What is the optimal testing algorithm for the assessment of Human Epithelial Growth Factor 2 (HER2) status in patients with GastroEsophageal Adenocarcinoma (GEA)?
• What strategies can help ensure optimal performance, interpretation, and reporting of established assays in patients with GEA?
Target Population: Patients with GEA.
Target Audience: Medical and surgical oncologists; oncology nurses and physician assistants; pathologists; general practitioners; and patients.
Key Points and Recommendations for Clinicians
For patients with advanced GEA who are potential candidates for HER2-targeted therapy, the treating clinician should request HER2 testing on tumor tissue.
Treating clinicians or pathologists should request HER2 testing on tumor tissue in the biopsy or resection specimens (primary or metastasis) preferably before the initiation of HERCEPTIN® therapy if such specimens are available and adequate. HER2 testing on fine-needle aspiration specimens (cell blocks) is an acceptable alternative.
Treating clinicians should offer combination chemotherapy and HER2-targeted therapy as the initial treatment of appropriate patients with HER2-positive tumors who have advanced GEA
Key Points and Recommendations for Pathologists
Laboratories/pathologists must specify the antibodies and probes used for the test and ensure that assays are appropriately validated for HER2 ImmunoHistoChemistry (IHC) and in situ hybridization (ISH) on GEA specimens.
When GEA HER2 status is being evaluated, laboratories/pathologists should perform/order IHC testing first, followed by ISH (In Situ Hybridization) when the IHC result is 2+ (equivocal). Positive (3+) or negative (0 or 1+) HER2 IHC results do not require further ISH testing.
Pathologists should use the Ruschoff/Hofmann method in scoring HER2 IHC and ISH results for GEA.
Pathologists should select the tissue block with the areas of lowest grade tumor morphology in biopsy and resection specimens. More than one tissue block may be selected if different morphologic patterns are present.
Laboratories should report HER2 test results in GEA specimens in accordance with the College of American Pathologists biomarker Template for Reporting Results of HER2 (ERBB2) Biomarker Testing of Specimens From Patients With Adenocarcinoma of the Stomach or Esophagogastric Junction.
Pathologists should identify areas of invasive adenocarcinoma and also mark areas with strongest intensity of HER2 expression by IHC in GEA specimens for subsequent ISH scoring when required.
Laboratories must incorporate GEA HER2 testing methods into their overall laboratory quality improvement program, establishing appropriate quality improvement monitors as needed to ensure consistent performance in all steps of the testing and reporting process. In particular, laboratories performing GEA HER2 testing should participate in a formal proficiency testing program, if available, or an alternative proficiency assurance activity.
There is insufficient evidence to recommend for or against genomic testing in patients with GEA at this time.
HER2 Testing and Clinical Decision Making in Gastroesophageal Adenocarcinoma: Guideline Summary From the College of American Pathologists, American Society for Clinical Pathology, and American Society of Clinical Oncology. Bartley AN, Washington MK, Ismaila N, et al. Journal of Oncology Practice 2017;13:53-57.