Despite the high mortality rate of ovarian cancer, there are few selective biomarkers that detect its progression and none have become successful targets for therapy. A complex microenvironment that promotes angiogenesis, reduces immune responses and alters the integrity of the surrounding matrix is involved through the biology of ovarian cancer. Previous studies done by our lab and collaborators indicated that extracellular threonyl-tRNA synthetase (TARS) is a pro-angiogenic mediator of the ovarian tumor microenvironment, which is secreted in response to inflammatory signals, and actively promotes angiogenesis. In order to better understand the mechanisms underlying the angiogenic effects of TARS in ovarian cancer, it is essential to identify whether it directly affects ovarian tumor growth and invasion. Preliminary evidence indicated that TARS is secreted from ovarian cancer cells in response to TNF-α and TARS exhibits extracellular angiogenic activity. In previous studies, TARS was shown to significantly increase migration of HUVECs in a transwell assay to an extent that was similar to VEGF. The purpose of this project was to establish a role for TARS in tumor progression and its potential as a diagnostic marker using an animal model of ovarian cancer. The hypothesis tested is that TARS plays a key role in the angiogenic and invasive potential of ovarian cancer, and TARS inhibition will reduce the angiogenic effect of tumor cells which is reflected by measurement of intratumor microvessel density (MVD). The study tested the effect of BC194-mediated TARS inhibition on the development of ovarian tumors in ID8 mouse model. We found a positive correlation between TARS expression and ovarian cancer progression, and TARS inhibition with BC194 reduce the progression of ovarian cancer. These data suggest that TARS has an important role in the tumor microenvironment and that TARS inhibition should be further investigated as a therapy for ovarian and other angiogenic cancers.