ERBB2 and breast cancer: The activation of HER2 signaling observed in approximately 20% of breast cancers, and overexpression of HER2 has also been described in a variety of other solid tumors, including gastric and gastroesophageal junction cancers, biliary tract cancer (BTC), colorectal cancer (CRC), non-small-cell lung cancer and bladder cancer, with incidences varying from greater than 50% of uterine cancers to around 2% of non-small-cell lung cancers (1).