Therefore, as previously shown in BC models19, our data provide evidence that d16HER2 may also be considered as a “flag” of HER2 addiction in GC as supported by the significant association we found between high d16HER2 score and prolonged PFS, and could be clinically investigated as a marker of trastuzumab susceptibility in several HER2-driven cancers, including CRC. This evidence concerns the gene ERBB2 and breast cancer.