As further proof of the suitability of the d16HER2 mRNA ISH score to quantify its expression levels in HER2-positive tumors, we observed a positive association between d16HER2 mRNA ISH score levels and qPCR values in human HER2-positive BC (Table 1; Fig. 3A) that became statistically significant in GC (Table 1, Fig. 3B; Score 2–3 versus Score 1: p = 0.0182; Score 2–3 versus Score 0: p = 0.0337). Here, ERBB2 is linked to gastric cancer.