9013 Background: ABT-510 is a 9-amino acid peptide that mimics the antiangiogenic activity of the naturally occurring protein, thrombospondin-1. In phase 1, ABT-510 was tolerated at doses up to 260 mg by subcutaneous injection (SC) per day. The pharmacokinetic target of 100 ng/mL for >3 hours was achieved at doses ≥20 mg daily. 15 patients with STS were included, with one confirmed partial response and 4 additional patients with stable disease >6 months. A phase 2 study evaluating the activity of ABT-510 in patients with relapsed or refractory STS has completed accrual. Methods: 88 patients with locally advanced or metastatic STS were randomized to receive 20 mg ABT-510 QD or 100 mg ABT-510 BID SC. Dosing is continuous. The primary endpoint of the study is progression-free survival (PFS); secondary endpoints include response rate, overall survival, and performance status. Tumor progression (by RECIST) is assessed every 8 wks. Circulating endothelial cells (CECs) are evaluated at baseline, 4 wks, then every 8 weeks. Safety is evaluated at every visit. Patients may remain on study until tumor size increases by 50% from baseline if there is clinical benefit and no other therapeutic options exist. Results: 44 men and 44 women were enrolled; 19 are active. The median age was 53 years (range 23–79); the baseline ECOG Performance Score for all patients was 0 or 1. Preliminary data for patients with prior cytotoxic chemotherapy (n=57) indicate a 6-month progression-free rate (PFR) of 34.4% (95% CI=18.2, 50.6) and without prior cytotoxic chemotherapy (n=25), 35.0% (95% CI=12.9, 57.2). No confirmed partial responses have been observed. Therapy was extremely well tolerated. Injection site reactions were the most frequently observed adverse event. Blinded data suggest a correlation of CEC concentration with duration of therapy; analysis is ongoing. Conclusions: The PFR seen in patients treated with ABT-510 exceeds the 14% rate reported for active drugs in STS by the EORTC and is suggestive of drug activity. Given the excellent safety profile and known antiangiogenic properties of ABT-510, further study is warranted for its use in the treatment of STS as a single-agent therapy or in combination with other active drugs. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Abbott Laboratories Abbott Laboratories Abbott Laboratories Abbott Laboratories