Abstract: The aim of this study was to investigate the effects of capsaicin on migration and invasion of breast cancer MDA-MB-231 cells and its possible mechanism.The MDA-MB-231 cells were incubated in the medium containing different concentrations of capsaicin for 24 h.CCK-8 assay was employed to detect the cell viability.The cell migration and invasion were assessed by wound healing assay and transwell invasion assay,respectively.The protein levels of c-Src,p-c-Src (Tyr416),FAK,p-FAK (Tyr576),Paxillin,p-Paxillin (Tyr118),matrix metalloproteinase 2 (MMP2) and MMP9 in the MDA-MB-231 cells were detected by Western blotting.The mRNA expressions of MMP2 and MMP9 were measured by RT-PCR.The result showed that capsaicin (25 and 50 μmol/L)remarkably reduced the abilities of migration and invasion (P < 0.05),inhibited the phosphorylation of c-Src,FAK and Paxillin (P <0.05),and down-regulated MMP2 and MMP9 expressions at mRNA and protein levels (P < 0.05) in MDA-MB-231 cells.These effects of capsaicin were all in dose-dependent manners.These results suggest that capsaicin may suppress the migration and invasion of breast cancer MDA-MB-231 cells by inhibiting the phosphorylations of c-Src,FAK and Paxillin,and down-regulating the mRNA and protein levels of MMP2 and MMP9.