The degree of angiogenesis in breast cancer has previously been shown to be an indicator of prognosis, and tumor microvasculature is at present a candidate target for new antiangiogenic therapies. Tie2/tek receptor tyrosine kinase is a novel marker of microvasculature of solid tumors that appears to play a key role in the angiogenesis process in breast cancer. However the prognostic significance of Tie2 has never been demonstrated in this neoplasm. In order to establish the prognostic value of Tie2 in breast carcinoma, we investigated Tie2 expression in a large series of patients and correlated it with long-term follow-up. Tie2 expression was investigated using immunohistochemical assays with a polyclonal antibody on frozen sections in a series of 909 patients, and was correlated with long-term (median, 11.3 years) follow-up. Univariate (Kaplan-Meier) analysis showed that a large Tie2 positive tumor surface (cut off = 7%) was significantly correlated with poor overall survival (p=0.025). Tie2 expression correlated with high metastasis risk among all patients (p=0.00067) and among node negative ones as well (p=0.01). Tie2 immuno-expression was also significantly predictive of relapse in all patients (p=0.003) and in the node negative subgroup (p=0.02). In multivariate analysis (Cox model) Tie2 immunodetection was identified as an independent prognostic indicator. Our results suggest that Tie2 immunohistochemical expression exhibits practical clinical relevance in terms of prognostic prediction. Tie2 expression permits identification of poor outcome patients, in particular node negative ones with high risk of metastasis and relapse. Tie2 immunodetection may further be considered as a potential tool for selecting patients who could benefit in the future from specific antiangiogenic therapy interfering with Tie2 pathway.