Moreover, it has yet to be defined which is the best therapeutic strategy as the response to anti-HER2 drugs is somehow “organ specific”; in fact, while Trastuzumab is effective in monotherapy in breast cancer, this is not true in HER2-amplified colon cancer, as demonstrated in Patient-Derived Xenografts (PDXs) preclinical models [39]. The gene discussed is ERBB2; the disease is breast carcinoma.