Stable knockdown of MMP-1 expression inhibits local tumor growth. A, each cell line was injected into mammary fat pads of nude mice (5×106 cells per mouse). Each group includes five mice. Asterisks indicate that the tumors of MMP-1 knockdown cell line sh1 grew significantly slowly than the control cell line shCtr (P < 0.05, t-test) and the tumors of MMP-1 knockdown cell lines sh1a and sh1b grew significantly slowly than those of the control cell line shNTC (P < 0.01, ANOVA Dunnett’s Multiple comparison test). B, real-time PCR quantification of MMP-1 mRNA levels of tumors showed a significant reduction in tumors of sh1 cells compared with shCtr tumors. C, representative MMP-1 immunohistological staining of tumor sections showing reduced staining in sh1 and sh1b tumors.