764 Background: Overexpression of the HER2 receptor protein predicts a worse prognosis and higher metastatic risk in patients (pts) with breast cancer. HER2 positivity also has a strong predictive value for the clinical benefit of trastuzumab (Herceptin, H). The aim of this study was to assess the incidence of HER2 and ER/PR overexpression in patients with newly diagnosed metastatic breast cancer (MBC) and to compare the characteristics and outcomes of pts with HER2-positive and HER2-negative disease. Methods: From June 2000 to November 2001, 96 centres in France participated in a prospective epidemiological study including 741 consecutive pts with newly diagnosed MBC. HER2 and hormonal receptor overexpression was assessed by immunohistochemistry (IHC). Results: Of the 699 evaluable pts aged 25 to 83 (median 54.6) years, 67% were postmenopausal. Tumour characteristics: 29.6% were HER2 3+ by IHC; 61.4% were ER+, and 66.6% either ER+ or PR+. Notably, 22.4% of ER+ and 21.3% of PR+ tumours were also HER2 IHC ...