We found that human DKK-1 can be detected in the blood of mice implanted with human osteosarcoma patient-derived xenografts, that treatment with BHQ880 dramatically reduces serum DKK-1 levels, modestly decreases primary tumor growth, and dramatically inhibits the development of metastases in mice whose tumors are completely resected. This evidence concerns the gene DKK1 and osteosarcoma.