HER2 amplification and/or overexpression have been described in BC (20% of cases) and in a variety of other solid tumors, including gastric cancer (GC, 20%), biliary tract cancer (BTC, 20%), bladder cancer (BlC, 12.5%), colorectal cancer (CRC, 5%) and NSCLC (2.5%) (33). This evidence concerns the gene ERBB2 and breast cancer.