Dasatinib is an orally active small molecule kinase inhibitor of both the src and abl proteins. To evaluate the potential role of dasatinib in breast cancer we used 39 human breast cancer cell lines that have been molecular profiled using Agilent Microarrays. They represent both luminal and basal breast cancer subtypes based on the relative gene expression of cytokeratin (CK) 8/CK18 and CK5/CK17, respectively, and those that have undergone an epithelial-to-mesenchymal transition (post-EMT) based on their expression of vimentin and the loss of CKs. When treated with 1 mICROM dasatinib in vitro 8 of them were highly sensitive (>60% growth inhibition), 10 of them were moderately sensitive (40-59% growth inhibition), and 21 were resistant to dasatinib. A highly significant relationship between breast cancer subtype and sensitivity to dasatinib was observed (chi2 = 9.66 and P = 0.008). Specifically, basal-type and post-EMT breast cancer cell lines were most sensitive to growth inhibition by dasatinib. In an attempt to identify potential predictive markers of dasatinib response other than breast cancer subtype we analyzed the baseline gene expression profiles for differentially expressed genes. We identified a set of three biologically relevant genes whose elevated expression is associated with dasatinib inhibition including moesin, caveolin-1, and yes-associated protein-1 with a sensitivity and specificity of 88 and 86%, respectively. Importantly, these data provide scientific rationale for the clinical development of dasatinib in the treatment of women with "triple-negative" breast cancer, a subtype that is categorized as being aggressive and lacking effective treatments (i.e. hormonal manipulation or trastuzumab).