Comparison of HER2 Status Before and After Trastuzumab-based Chemotherapy in Patients With Advanced Gastric Cancer

Background/Aim: The aim of the present study was to compare human epidermal growth factor receptor 2 (HER2) expression before and after trastuzumab-based chemotherapy in patients with advanced HER2-positive gastric cancer. Materials and Methods: We assessed HER2 expression using immunohistochemistry and/or fluorescence in situ hybridization in pre-treatment biopsied specimens and post-treatment resected specimens obtained from seven patients with advanced HER2-positive gastric cancer receiving trastuzumab-based chemotherapy. Results: Four patients maintained the HER2-positive status and three patients had a change in HER2 expression from positive to negative. In patients showing the loss of HER2 expression after treatments, HER2-positive tumor cells with a dominant histological type disappeared, and HER2-negative tumor cells with another dominant histological type were identified. Conclusion: HER2 expression can change after trastuzumab-based chemotherapy in patients with advanced HER2-positive gastric cancer. Continuous monitoring of HER2 expression after treatments may be utilized to determine whether the continued use of trastuzumab is advisable.