We assume that trastuzumab is more effective in HER2 homogeneity patients and less effective in HER2 heterogeneity patients, indicating that it may not be possible to observe differences in the effect of trastuzumab in HER2 homogeneity BC patients receiving postoperative trastuzumab administration, although this should be evaluated in future studies. This evidence concerns the gene ERBB2 and breast cancer.