I n human breast cancer, loss of carcinoma cell–specific response to TGF-β signaling has been linked to poor patient prognosis. However, the mechanisms through which TGF-β regulates these processes remain largely unknown. In an effort to address this issue, we have now identified gene expression signatures associated with the TGF-β signaling pathway in human mammary carcinoma cells. The results strongly suggest that TGF-β signaling mediates intrinsic, stromal-epithelial, and host-tumor interactions during breast cancer progression, at least in part, by regulating basal and oncostatin M–induced CXCL1, CXCL5, and CCL20 chemokine expression. To determine the clinical relevance of our results, we queried our TGF-β–associated gene expression signatures in 4 human breast cancer data sets containing a total of 1,319 gene expression profiles and associated clinical outcome data. The signature representing complete abrogation of TGF-β signaling correlated with reduced relapse-free survival in all patients; however, the strongest association was observed in patients with estrogen receptor–positive (ER-positive) tumors, specifically within the luminal A subtype. Together, the results suggest that assessment of TGF-β signaling pathway status may further stratify the prognosis of ER-positive patients and provide novel therapeutic approaches in the management of breast cancer.