Galectin-1, a carbohydrate-binding protein, abundantly expressed at sites of tumor growth and metastasis, promotes tumor progression by influencing diverse cancer-related events including tumor cell migration, angiogenesis, and tumor-immune escape. Dalotto-Moreno and colleagues show that galectin-1 contributes to immunosuppression during progression of breast cancer. Human breast cancer biopsies expressed substantial amounts of galectin-1, which positively correlated with tumor grade. Silencing Gal1 expression in the 4T1 breast tumor model reduced tumor growth and lung metastases. This effect was accompanied by a diminished frequency and suppressive activity of CD4⁺CD25⁺ Foxp3⁺ regulatory T cells in both the tumor and metastatic lungs. For details, see article by Dalotto-Moreno and colleagues on page 1107.