Abstract Osteosarcoma is the most common malignant bone tumor in children and young adults. Despite the use of multi-agents chemotherapy and aggressive surgery, the survival of patients with osteosarcoma remains at 60% over the past three decades. In addition, the survival of patients who develop metastasis is dismal and often less than 25%. We have previously reported that serum C-X-C motif chemokine ligand 10 (CXCL10) is associated with survival in a large cohort of osteosarcoma patients. CXCL10 is an interferon-induced chemokine that binds to its cognate receptor CXCR3 to elicit its cellular effects via both autocrine and paracrine signaling. CXCL10 can promote tumor cell migration and metastasis via autocrine signaling, while it recruits CXCR3+ immune cells to exert a tumoricidal effect via paracrine signaling. However, little is known about the effect of circulating CXCL10 in cancer. To understand the role of CXCL10 in the pediatric bone tumor, we showed that a number of osteosarcoma cell lines expressed the CXCR3 protein. The addition of exogenous CXCL10 promoted tumor cell migration of three osteosarcoma cell lines but did not affect cell proliferation. However, the migratory effect of osteosarcoma cells is not specific to CXCL10, as other CXCR3-associated chemokines (CXCL4, CXCL9, and CXCL10) exerted similar effects. Using an orthotopic xenograft mouse model, we demonstrated intravenous injection of CXCL10 increased the development of pulmonary metastases of osteosarcoma. In contrast, expression profiling of osteosarcoma primary tumors showed that elevated expression of CXCL10 and CXCR3 was associated with a better prognosis, suggesting that a paracrine effect of CXCL10 by recruiting CXCR3+ immune cells to the tumor site. This notion is supported by our immune cell population deconvolution results, indicating that the predominant infiltrating immune cell types are macrophages and CD8+ T cells. Taken together, our results suggest a model in which CXCL10 may play both pro-tumor and anti-tumor roles in osteosarcoma. While a high level of exogenous or circulating CXCL10 may promote tumor cell migration and metastasis, the chemokine can also recruit CXCR3+ immune cells to exert a favorable prognostic effect. Further characterization of the sources of CXCL10 in the tumor site and circulation may lead to the development of a therapeutic approach that promotes CXCL10’s anti-tumor effects and minimizes its pro-tumor effects to improve the survival of osteosarcoma patients. Citation Format: Xiang Chen, Margaret Clement, John Hicks, Tsz Kwong Man. The dual roles of C-X-C MOTIF chemokine LIGAND 10 in pediatric osteosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6092.