Since MMP9, a gelatinase involved in tumor invasion, exhibits the second largest expression difference (a 15.28-fold difference) among the MMP family members in osteoblasts between Osx-knockout mice and Osx-wild-type mice24, we hypothesized that Osx promotes invasiveness of breast cancer cells by upregulating MMP9 expression. This evidence concerns the gene MMP9 and breast carcinoma.