CAP, ASCP, and ASCO have published a clinical guideline on HER2 testing and clinical decision making in gastroesophageal adenocarcinoma. Noting that there are no comprehensive guidelines for the assessment of HER2 in patients with gastroesophageal adenocarcinoma, the panel recommends that:

• Tumor specimens from all patients with advanced gastroesophageal adenocarcinoma, who are candidates for HER2-targeted therapy, should be assessed for HER2 status before the initiation of HER2-targeted therapy.
• Clinicians should offer combination chemotherapy and a HER2-targeted agent as initial therapy for all patients with HER2-positive advanced gastroesophageal adenocarcinoma.

Additionally, for pathologists, guidance is provided for morphologic selection of neoplastic tissue, testing algorithms, scoring methods, interpretation and reporting of results, and laboratory quality assurance.