Objective: To explore the relationship between tumor size and response to combined anti-vascular targeted therapy using the anti-angiogenesis inhibitor, bevacizumab, and the tubulin-binding vascular disrupting agent, fosbretabulin.
Methods: An exploratory, post-hoc analysis of the randomized phase II trial, Gynecologic Oncology Group-0186I, was performed. One hundred and seven patients with recurrent ovarian carcinoma, treated with up to 3 prior regimens, were randomized to bevacizumab 15 mg/kg body weight with or without intravenous fosbretabulin 60 mg/m2 body surface area every 21 days until progression or unacceptable toxicity. The primary analysis favored the combination (HR 0.69; 95% CI, 0.47-1.00; p = .049) [Monk BJ, et al. J Clin Oncol 2016;34:2279-86]. The Cox proportional hazards model was used to estimate the treatment effect in various subpopulations.
Results: With extended follow-up, the median PFS for bevacizumab plus fosbretabulin was 7.6 months as compared to 4.8 months with bevacizumab alone (HR 0.74; 90% CI, 0.54-1.02). Overall survival was similar in the experimental and control arms (25.2 vs 24.4 mos, respectively, HR 0.85; 90% CI, 0.59-1.22; p = .461). Eighty-one patients had measurable disease and median tumor size was 5.7 cm. In the ≤5.7 cm subgroup, the HR for progression or death was 0.77 (90% CI 0.45-1.31). Patients with tumors >5.7 cm (n = 40) had a HR for progression or death of 0.55; 90% CI, 0.32-0.96; p = .075).
Conclusions: Although no significant survival benefit was observed, the trend showing a reduced HR for progression or death with increasing tumor size when fosbretabulin is added to bevacizumab compared to bevacizumab alone warrants further study.
Keywords: Bevacizumab; Fosbretabulin; Ovarian cancer; Vascular disrupting agent.
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