Resistance to trastuzumab may also occur through HER2 receptor mutation, such as amino-truncation (27, 28): p95HER2 is an amino-truncated form of the HER2 receptor that lacks the trastuzumab binding site and is found in 60–77% of HER2-positive oesophago-gastric cancer patients (27, 28). This evidence concerns the gene ERBB2 and gastric cancer.