1. Introduction
Human epidermal growth factor receptor 2 (HER2) is
amplified and/or overexpressed in approximately 20% of
breast cancers [1e3]. A number of studies suggest that
amplification of HER2 is a very early event in the
development of invasive carcinomas and it is usually
maintained throughout the natural history of the
tumour [4,5]. All newly diagnosed breast cancers are
tested for HER2 overexpression using immunohistochemistry
(IHC) and/or in situ hybridisation (ISH)