To first assess the effect of T-DXd on cell proliferation of HER2-positive and HER2-negative GC cells, three HER2-amplified GC cell lines (NCI-N87, OE19, and MKN7) and two HER2-non-amplified GC cell lines (AGS and NUGC3) were used in this study (Fig. 1A). Here, ERBB2 is linked to gastric cancer.