Matrix Metalloproteinase-2 (MMP-2) is an enzyme that degrades components of the extracellular matrix and thus plays a pivotal role in cell migration during physiological and pathological processes (e.g. gastric, pancrcreatic, prostate, and breast cancer). MMP-2 expression is dependent on extracellular matrix metalloproteinase inducer (EMMPRIN), Her2/neu, growth factors, cytokines, and hormones. Pro-MMP-2 activation needs MT1-MMP and TIMP-2 contribution. The active forms of MMPs subsequently release a cascade of activation of the remaining pro-MMPs. Inactivation of the physiological function of MMPs, or even pro-MMPs, is accomplished by non-covalent TIMP binding. The detection of active MMP-2 alone or the rate of pro-MMP-2 and active MMP-2 is considered a very sensitive indicator of cancer metastasis. Modulation of MMP-2 expression and activation through specific inhibitors and activators may thus provide a new mechanism for breast cancer treatment. Degradation of the cellular network established by adhesion molecules such as E-cadherin or ALCAM/CD166 causes tumor tissue relaxation, increases metastasis, and correlates with shortened survival in patients with primary breast carcinoma. A low level of MMP-2 is linked to favorable prognosis in patients with a hormone receptor-negative tumor, usually associated with high risk. Blocking MMP-2 secretion and activation during breast carcinoma development may decrease metastasis. Besides zoledronic acid and bisphosphonates, the new synthetic metalloproteinase blockers (MMPIs) batimastat, marimastat, and tetracycline derivates have been investigated in anticancer therapy. Recent research shows that modified synthetic siRNA targeting TIMP-2 may also regulate the balance between MMPs and TIMP-2 and thus decrease the degradation of extracellular matrix and prevent distant metastasis.