['Angiopoietin-2 (Ang-2) plays critical roles in vascular morphogenesis and its upregulation is frequently associated with various tumors. Previous studies showed that certain selenium compounds possess anti-tumor effects. However, the underlining mechanism has not been elucidated in detail. Plus, results of research on the anti-tumor effects of selenium compounds remain controversial.', 'We investigated levels of Ang-2 and vascular endothelial growth factor (VEGF) on the estrogen-independent bone metastatic mammary cancer (MDA-MB-231) cells in response to treatment by methylseleninic acid (MSeA), and further examined the effects of MSeA oral administration on xenograft mammary tumors of athymic nude mice by RT-PCR, Western, radioimmuno assay, and Immunohistochemistry.', 'Treatment of MDA-MB-231 cells with MSeA caused significant reduction of Ang-2 mRNA transcripts and secretion of Ang-2 proteins by the cells. Level of VEGF protein was accordingly decreased following the treatment. Compared with the controls, oral administration of MSeA (3 mg/kg/day for 18 days) to the nude mice carrying MDA-MB-231 induced tumors resulted in significant reduction in xenograft tumor volume and weights, significant decrease in microvascular density, and promotion of vascular normalization by increasing pericytes coverage. As expected, level of VEGF was also decreased in MSeA treated tumors.'] Does methylseleninic acid restrict tumor growth in nude mice model of metastatic breast cancer probably via inhibiting angiopoietin-2?