Tenascin-C is an extracellular matrix molecule that drives progression of many types of human cancer, but the basis for its actions remains obscure. In this study, we describe a cell-autonomous signaling mechanism explaining how tenascin-C promotes cancer cell migration in the tumor microenvironment. In a murine xenograft model of advanced human osteosarcoma, tenascin-C and its receptor integrin alpha9beta1 were determined to be essential for lung metastasis of tumor cells. We determined that activation of this pathway also reduced tumor cell-autonomous expression of target genes for the transcription factor YAP. In clinical specimens, a genetic signature comprising four YAP target genes represents prognostic impact. Taken together, our results illuminate how tumor cell deposition of tenascin-C in the tumor microenvironment promotes invasive migration and metastatic progression.Significance: These results illuminate how the extracellular matrix glycoprotein tenascin-C in the tumor microenvironment promotes invasive migration and metastatic progression by employing integrin alpha9beta1, abolishing actin stress fiber formation, inhibiting YAP and its target gene expression, with potential implications for cancer prognosis and therapy. Cancer Res; 78(4); 950-61. (c)2017 AACR.