MMP2 and cancer: Various in vitro and in vivo assays highlight that ginsenosides including compound K (CK), Rg1, Rg3, Rh1, Rh2 and Rd reduced metastatic abilities of various tissue-specific cancer cells by down-regulating the transcriptional expressions of several MMPs (MMP-1, MMP-2, MMP-3, MMP-7, MMP-9 and MMP-13).