Hepatoma-derived growth factor (HDGF) has been implicated in the growth and metastasis of various types of human cancer, but the role of HDGF expression in prostate cancer or breast cancer has not been documented. To assess the role of HDGF in the proliferation, migration and invasion by prostate and breast cancer cells, HDGF expression in DU145 and MCF7 cells was knocked down using siRNA, and the effect of such knockdown was assessed by MTS and [3H]-thymidine incorporation Transwell assays. Moreover, we identified differentially expressed genes that might mediate the HDGF-induced cellular effects. Our results demonstrate that down-regulation of HDGF expression significantly reduces the proliferation of both DU145 and MCF7 cells. However, down-regulation of HDGF expression in DU145 inhibited cell migration and invasion, but in MCF7 cells it stimulated cell migration and invasion. This differential effect might result from the differential induction of PIK3R1 or SERPINE1 in the two cell lines upon HDGF-siRNA treatment. In conclusion, HDGF may participate in the pathogenesis of prostate and breast cancer by promoting cell growth and it may be a therapeutic target for these cancers.