ERBB2 and breast cancer: HER2 protein overexpression, gene amplification and mutation have been identified in a variety of cancer types which include breast cancer, gastrointestinal cancers like gastric, colorectal cancers, pancreatic cancer, oesophageal, biliary tract cancers lung cancer, salivary gland tumours, gynaecological cancers like ovarian, cervical, endometrial cancers and vulvar Paget’s disease, bladder and head and neck squamous cell carcinoma [16, 22, 27–30].