Suppression of CDC25B expression by siRNA2-CDC25B delayed tumor progression in a xenograft model. Hep40 cells were subcutaneously inoculated into the flanks of 10 mice (107 for each). When the tumor size reached an average of 200 mm3, 5 mice were given 8 μl RNAiMAX diluted to 30 μl with PBS, and another 5 mice given 5 μg siRNA and 8 μl RNAiMAX diluted to 30 μl with PBS by intratumor injection every two days. The tumor volume was assessed before each injection using a digital caliper. Significant differences in the tumor volumes of both groups were observed beginning from day 7 of siRNA2-CDC25B injection (P < 0.05). Columns, mean of the tumor size of five mice; bars, SD.