Especially, LCB‐ADC shows good efficacy in terms of suppressing tumor growth in a patient‐derived xenograft (PDX) model of HER2‐positive gastric cancer as well as in T‐DM1‐resistant models such as HER2 low‐expressing HER2 low expressing JIMT‐1 xenograft tumor and PDX. Here, ERBB2 is linked to gastric cancer.