We demonstrated that TNBC cell–derived exosomes are a factor in the induction of M2-type macrophage polarization (upregulation of CD206 and arginase-1) to the benefit of breast cancer cells in vitro and in vivo, supporting enhanced tumor growth and axillary LN metastasis in an orthotopic TNBC model. The gene discussed is ARG1; the disease is breast carcinoma.