This latter subtype accounts for 20–30% of all invasive BCs and it is characterized by a remarkably high expression of HER2, an orphan tyrosine kinase receptor involved in proliferation signalling, varying from 500.000 to more than 2 million molecules per cell compared to the 25.000 to 185.000 present in normal epithelial cells or non-amplified tumours [3]. The gene discussed is ERBB2; the disease is neoplasm.