Gastric Cancer HER2 IHC Assessment

Clinical significance of HER2 in gastric cancer

With the potential to inform treatment options, HER2 testing is of vital importance in enabling us to learn more about patients' gastric cancer.¹ To support HER2 IHC clinical practice, the ASCO-ASCP-CAP joint committee have published extensive testing guidelines, which cover pre-analytics, scoring, and reporting recommendations.¹

View guidelines

How does HER2 in gastric cancers differ from breast?

Membranous distribution of antibody

Breast

Predominantly circumferential in IHC 3+^2,3

Gastric

Can be basolateral or lateral in IHC 3+^1,2

Intratumoral heterogeneity

Breast

Less commonly encountered⁴

Gastric

More commonly encountered⁴

Location dependent variation in
HER2
expression

Does not occur²

More frequent in the proximal stomach
relative
to distal²

Gastric HER2 IHC scoring algorithm

ASCO-ASCP-CAP guidelines recommend the following scoring algorithm for gastric cancers, which define separate scoring criteria for surgical and biopsy specimens.

View scoring algorithm

*Tumor cell cluster (≥5 neoplastic cells).

Images supplied by Discovery Life Sciences, Inc.

Adapted from Bartley, et al. J Clin Oncol. 2017;35(4):446-464.

Testing and reporting guidelines

Testing method

IHC with reflex to ISH for equivocal (IHC 2+) results.¹

Reporting

CAP have published a template for gastric HER2 biomarker reporting⁵

Key reporting elements

Discrete HER2 IHC score⁵
HER2 (ERBB2) ISH result⁵
HER2 (ERBB2) genomic test results⁵
Methods⁵

ASCO, American Society of Clinical Oncology; ASCP, American Society for Clinical Pathology; CAP, College of American Pathologists; ERBB2, erythroblastic leukemia viral oncogene homolog 2; GEA, gastroesophageal adenocarcinoma; HER2, human epidermal growth factor receptor 2; IHC, immunohistochemistry; ISH, in situ hybridization.

1. Bartley AN, et al. J Clin Oncol 2017;35(4):446-464. 2. Abrahao-Machado LF and Scapulatempo-Neto C. World J Gastroenterol 2016;22(19):4619-4625. 3. Wolff AC, et al. Arch Pathol Lab Med 2023;147(9):993-1000. 4. Kaito A, et al. World J Clin Cases 2019;7(15):1964-1977. 5. CAP. Template for Reporting Results of HER2 (ERBB2) Biomarker Testing of Specimens from Patients with Adenocarcinoma of the Stomach or Gastroesophageal Junction. Version 1.0.0.1. Accessed: January 2024. Available at: https://documents.cap.org/protocols/cp-gastric-HER2biomarker17-1001.pdf.