Introduction

HER2 overexpression occurs in approximately 15-20% of pts with breast cancer and is associated with aggressive disease and decreased survival. HER2 status is predictive of response to trastuzumab and lapatinib. Given the importance of HER2 positive disease, accurate evaluation of HER2 status is essential. The aim of this study is to provide insights into the relationship between HER2 expression by immunohistochemistry, DNA microarray and FISH in a large cohort of 1,032 breast cancers. HER2 protein expression were determined using antibody clones (4B5) and interpreted per ASCO/CAP scoring criteria. Samples scored as equivocal (>=2+;> 10% to <+3+; <=30%) were required to undergo further assessment with FISH HER2 testing (Pathvysion). All samples were tested for HER2 by DNA microarray provided there was sucient quantity of RNA in all tumor samples.