Using TA3 murine mammary carcinoma cells, Yu and Stamenkovic (20) showed that MMP9 is localized on the cell surface in a CD44-dependent manner and stimulates proteolytic cleavage of TGF-β, and they proposed a novel role for MMP9 in TGF-β-dependent tumorigenesis. The gene discussed is TGFB1; the disease is breast carcinoma.