Intratumoral HER2 heterogeneity may have influenced the inconsistencies in these results between breast and gastric cancers despite their having the same HER2 property: the median proportion with HER2 amplification by FISH was 87.8% in breast cancer, whereas, in gastric cancer, almost half of the patients with HER2 protein overexpression exhibited it in less than 30% of the tumor cells [21, 23]. Here, ERBB2 is linked to gastric cancer.