Macrophage Stimulating Protein (MSP) is the only known ligand for the receptor tyrosine kinase Ron. The MSP/Ron pathway is involved in several important biological processes, including macrophage activity, wound healing, and epithelial cell behavior. A role for MSP/Ron in breast cancer has recently been elucidated, wherein this pathway regulates tumor growth, angiogenesis, and metastasis. Here, we review the recent literature surrounding MSP/Ron function in tumor cells, inflammatory cells, and osteoclasts – cell types that often coexist in breast tumor microenvironments. We discuss the potential implications of MSP/Ron activity occurring concurrently in these cell types on tumor progression and metastasis. Lastly, we outline the potential for targeting MSP/Ron as a novel therapy for breast cancer, and for other cancer types.