Chemerin treatment inhibited RANKL-induced osteoclast formation and bone resorption by reducing the secretion of matrix metalloproteinase (MMP)-2, MMP-9, and cathepsin K. Intraperitoneal administration of chemerin inhibited tumor growth in MCF-7 breast cancer cell-injected mice and reduced the development of osteolytic lesions resulting from intratibial inoculation of MDA-MB-231 cells. This evidence concerns the gene MMP9 and breast cancer.