Interestingly, HER2 overexpression rate progressively increases moving from the poorly cohesive WHO histotype to the mitochondrion-rich adenocarcinoma (MRC), tubular adenocarcinoma, and hepatoid carcinoma (HAS) [74, 76] which has the highest frequency of HER2 positivity and the worst prognosis [74, 76]. The gene discussed is ERBB2; the disease is adenocarcinoma.