MMP9 and neoplasm: In addition, we investigated the expression of matrix metalloproteinases (MMPs), which promote invasion and metastasis of tumor cells by degrading the extracellular matrix, and found that silencing of CR-1 expression significantly down-regulated MMP9 expression at both mRNA and protein levels (Fig. 3g and Additional file 1: Figure S4), whereas the expression of MMP2 and MMP7 was not been affected.