Abstract
97 Background: Three angiogenesis-related serum biomarkers [TIMP-1 (tissue inhibitor of metalloproteinase-1), CA IX (carbonic anhydrase 9), and VEGF] and PSA were correlated with outcome in the phase II zibotentan [endothelin A (ETA) receptor inhibitor] trial in metastatic CRPC. Methods: Pretreatment serum samples were available from 206 of 312 patients enrolled in the multicenter phase II trial evaluating zibotentan in patients with metastatic CRPC and bone metastases who were pain free or mildly symptomatic for pain, with a 1:1:1 randomization to zibotentan 10mg, 15mg, or placebo. The CA IX, TIMP-1, and VEGF ELISAs were from WILEX Inc./ Oncogene Science, Cambridge, MA. Progression-free survival (PFS) and overall survival (OS) were analyzed using the Kaplan-Meier method and Cox modeling. Results: In the final efficacy report, there were no statistical differences in PFS, but a trend for OS improvement was observed in the zibotentan arms compared with placebo: 15 mg (HR 0.76; 80% CI 0.61–0.94; p= 0.103) and 10 mg (HR 0.83; 80% CI 0.67–1.02; p= 0.254) (James et al, BJUI 106L966-973, 2010). In the retrospective serum biomarker analysis (206 patients), there were no apparent differences for PFS with any of the 3 novel biomarkers in the whole population, or within treatment arms. For OS in the whole population, patients with higher serum TIMP (> median) had reduced OS (17.5 mos), compared with patients who had lower serum TIMP-1 (< median) (28.4 mos). Within treatment arms, patients with higher serum CA IX (> median) treated with zibotentan had increased OS in both the 10 mg arm (median 28.4 mos), and the 15 mg arm (median 25.7 mos) compared with those in the placebo arm (median 15.4 mos). In a Cox model, including serum biomarkers and bisphosphonate use, for PFS only PSA was significant (p< 0.0001); for OS only PSA (p< 0.0001) and TIMP-1 (p< 0.002) were significant. Conclusions: Higher pretreatment serum CA IX (a marker of hypoxia) may identify a cohort of metastatic CRPC patients more sensitive to zibotentan treatment, and higher serum TIMP-1 may identify patients at risk for reduced overall survival. These serum biomarkers deserve further study in larger ETA receptor inhibitor trials.
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