Understanding the molecular background of breast cancer biology is critical in developing new biomarkers for earlier diagnosis and more optimized treatment. We performed a proteomic analysis of human breast carcinoma tissues to investigate the tumor-specific protein expression in breast carcinoma. Using 2-dimensional electorphoresis (2-DE) and matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS), we were able to identify a list of proteins which are upregulated in cancerous tissue. There was significant increase of galectin-1 expression in all cancerous tissues compared to noncancerous tissues, and its increased expression was further confirmed by western blot immunostaining. Subsequent immunohistochemical staining against galectin-1 in 105 breast cancer specimens showed significant correlation between galectin-1 expression in cancer-associated stromal cells and tumor invasiveness, T stage, TNM stage, and axillary lymph node metastasis. Galectin-1 expressionin cancer cells showed no correlation to above-mentioned pathologic variables. Hormonal receptor status and galectin-1 expression showed no correlation. This study demonstrates the upregulation of galectin-1 in breast carcinoma tissues and the clinical significance of galectin-1 in breast cancer patients. Our data supports the recently highlighted roles of galectin-1 in cancer-associated stroma and in tumor immune privilege.