Aberrant microenvironments and loss of balance in cell-extracellular matrix signaling are associated with breast cancer invasion, metastasis, and resistance to therapy. We have recently shown that increased beta1 integrin signaling is involved in malignant progression and that inhibitory antibody to beta1 integrin leads to selective apoptosis and decreased proliferation in three-dimensional cultures and in xenograft models of breast cancer in vivo. To investigate the clinical importance of these findings, in the present study we examined the expression of beta1 integrin and extracellular beta1 integrin ligands fibronectin and laminin-1 in a cohort of 249 breast cancer patients who had a median follow-up of 8.4 years. Among the 149 scorable cases, the highest beta1 integrin intensity score (3+ versus 0-2+) was associated with significantly decreased 10-year overall survival of 48% versus 71% (P<0.03) and decreased disease-free survival of 50% versus 80% (P<0.05). Importantly, high fibronectin expression was associated with decreased overall and disease-free survival on univariate analysis (P<0.04) and beta1 integrin intensity score was significantly correlated with fibronectin expression (Kendall's tau-b=0.19; P=0.03). In a multivariate Cox proportional hazards model, beta1 integrin intensity score remained a significant independent predictor of overall survival [hazard ratio (HR), 1.69; 95% confidence interval (95% CI), 1.19-2.38; P<0.003] and disease-free survival (HR, 1.87; 95% CI, 1.21-2.88; P<0.005). These findings show that beta1 integrin expression has potential prognostic value in invasive breast cancer and that coexpression of fibronectin may help identify patients with more aggressive tumors who may benefit from targeted therapy.