ERBB2 and invasive breast carcinoma: Gene amplification of HER2 (HER2/neu, c-erbB2) receptor tyrosine kinase (RTK) is found in 10 to 25% of invasive breast carcinomas [1,2] and is associated with an unfavourable impact on the course of disease and reduced responsiveness to tamoxifen therapy, for example [3,4].