Abstract: Objective: To investigate the function of NT21MP from human herpesvirus-8(HHV8) monocyte inflammatory protein(MIP) N-terminal peptide in resisting breast cancer.Methods: Breast carcinoma model mice were established by 4T-1 breast cancer cell strains.The models were divided into NT21 MP group(5μg/kg,50μg/kg and 500 μg/kg),combination therapy group(NT21MP 50 μg/kg + Herceptin 36.04 μg/kg).positive control group(Herceptin 36.04 μg/kg) and sodium chloride group.The size of the tumor on the tumor-bearing mice was observed,the tumor inhibitory rate was calculated and the metastasis lung node was detected.Results: Compared with the tumor-bearing mice in sodium chloride group,NT21 MP inhibited the growth of tumor in a dose-dependent manner,which was the most evident in the combination group(P < 0.01).The tumor inhibitory rates in the NT21MP groups with different concentrations,the combination group and the positive control group were 10.0%,41 6%,81.0%,58.2% and 39.2% respectively.Metastasis Lewis lung cancers were observed in both of the control groups,and several metastasis nodes of white tumor were observed on the surface of the mice's lung;and the situation was the same with NT21MP 5 μ/kg group.In NT21 MP 50 μg/kg group and Herceptin group,metastasis Lewis lung cancers were noted in the lungs of five sixths of the mice,and small and single metastasis node was found on the surface of the lung.In the NT21 MP 500 μg/kg group and the combination therapy group,metastasis Lewis lung cancers were noted in two sixths and three sixths of the mice,respectively,and no obvious metastasis nodes were found on the surface of the mice's lung.Conclusions: NT21MP may inhibit the growth and metastasis of breast cancer.Combination therapy of NT21 MP and the targeted drug Herceptin can improve the clinical efficacy.