For example, some intrinsic resistance mechanisms affect the ability of HER2 inhibitors to directly engage HER2 in BC; a truncated form of HER2, p95, lacking the trastuzumab binding region [24,25]; a splice variant that eliminates exon 16 (HER2-Δ16) in the extracellular domain of the HER2 receptor, preventing disruption of HER2 homodimers upon binding by trastuzumab [26]; In our study, we did not assess p95, but we did find HER2-Δ16 in a GC tumor sample, which naturally harbored HER2-Δ16. This evidence concerns the gene ERBB2 and breast cancer.