SPARC and breast cancer: For example, versican, a matrix proteoglycan, is produced by monocytes in pre-metastatic lesions where it aids breast cancer cell transformation in MMTV-PyMT mice (51), whilst expression of the ECM glycoprotein SPARC (secreted protein acidic and rich in cysteine) by breast tumor cells induces EMT dependently on the presence of MDSC (52) in breast cancer cell engraftment, and expression of SPARC by macrophages induces cell migration and metastasis in triple-negative breast cancer cells engraftment (50).