GASTric Cancer HER2 Re-Assessment Study 2 (GASTHER2): HER2 Re-Assessment for Initially HER2 Negative Advanced Gastric Cancer Patients After Progression on First-Line Treatment.

Overall, 4.0% of patients with baseline HER2-negative AGC were HER2-positive on re-assessment, and the HER2 positive re-assessment rate was higher among patients who had a single test at baseline. HER2 re assessment may be considered for initially HER2 negative patients to determine their eligibility for HER2-directed therapy, particularly if their HER2 negativity was determined by a single test, especially if they had a single baseline HER2 IHC 1+ test.