ObjectiveWe used the RNAi technology to silence cell signal transducer and activator of transcription 3 (STAT3) gene to investigate the intratumoral injection of siRNA and by intraperitoneal injection of two ways on the impact of breast cancer xenografts in nude mice.MethodsWe cultured MCF-7 breast cancer cells and implanted in subcutaneously in the back of the female nude mice, producing breast cancer tumor model in nude mice. When the tumor grew to a certain size, they were randomly divided into control intratumoral injection of group(A group), intraperitoneal injection of control group(B group), intratumoral injection group(C group) and injected group(D group), according to plasmid quality as 20μg/0.2ml/dose only to tumor injection and intraperitoneal injections were injected into the C, D each group of nude mice, A, B means nude mice were injected with saline according to the corresponding methods. After the transfection,tumor growth was observed every other day, when the A group or B group reached the tumor volume is large enough (≥500mm3), all mice were put to death,and got the tumor. its size and weight were measured, the line Immunohistochemical staining, Western Blot and RT-PCR, the expression of STAT3, compare the differences between groups. ResultsSTAT3 in the dsRNA will carried in the plasmid in two different ways within the tumor cells into nude mice, both groups showed significant inhibition of tumor growth occurred, the difference with the control group were statistically significant (P<0.05), but in the two control groups and two experimental groups, there was no significant difference(P>0.05). Analysis at the protein level, the two experimental groups decreased STAT3 protein expression (P<0.05), but there was no significant difference between two experimental groups (P>0.05). Determined from the analysis of STAT3, two experimental groups decreased STAT3 gray values (P<0.05), there was no significant difference between two experimental groups (P>0.05). In immunohistochemical analysis, the two blocks of the experimental groups showed significant tumor cell necrosis, and intratumoral injection group appeared in the center of the tumer showed negative STAT3 but the surrounding appeared positive.ConclusionsUse the RNA interference technology, through intratumoral injection and intraperitoneal injection of two ways can be silenced the STAT3 gene, inhibition of its expression and tumor growth, but between the two approaches there was no significant difference.