Patients receive cilengitide IV over 1 hour on days 1, 4, 8, 11, 15, 18, 22, and 25. Treatment repeats every 28 days for at least 3 courses in the absence of disease progression or unacceptable toxicity. After 3 courses, patients undergo evaluation. Patients achieving a complete prostate-specific antigen (PSA) response (i.e., PSA < 0.2 ng/mL) receive 2-3 additional courses of therapy. Patients with partial PSA response or stable disease continue treatment indefinitely in the absence of disease progression or unacceptable toxicity. Patients demonstrating disease progression by CT scan, MRI, or bone scan are removed from the study.