Abstract
5013 Background: Therapeutic poxviral vaccines for prostate cancer are safe with preliminary evidence of clinical benefit in phase I/II studies. PROSTVAC-VF (PV) comprises 2 recombinant viral vectors (Vaccinia and Fowlpox), each encoding transgenes for prostate specific antigen (PSA) and 3 immune costimulatory molecules (B7.1, ICAM-1, and LFA3: TRICOM). PV is administered subcutaneously in a heterologous prime-boost regimen with concurrent low-dose GM-CSF. Methods: 122 patients (pts) were treated in a multi-center, double-blind, RCT of a vaccination series. Pts were randomized 2:1 to PV + GM-CSF vs. placebo empty vector + control saline injections (C). Vaccinia-based vector was used for priming followed by 6 planned Fowlpox-based vector boosts. The trial completed enrollment in July 2005. Eligible pts had metastatic disease, a rising PSA despite castrate testosterone levels, and a Gleason score of ≤7. Pts with a history of prior chemotherapy use, visceral metastasis, or narcotic use were excluded. The 1º endpoint was progression free survival (PFS), with progression defined as 2 new lesions on bone scan or RECIST-defined progression. Vaccination was discontinued after progression. Results: 82 pts received PV and 40 received C. Pt characteristics were similar (means): age (72PV/76C), PSA (134PV/188C), Alk-Phos (142PV/159C), LDH (207PV/218C), Hgb (13PV/13C), and number bone metastatic sites (5.3PV/6.5C). Mean number of vaccinations was 5.4 PV and 5.3 C. PFS was similar in the 2 groups (p = 0.56). However, at 3 years post study, PV patients had a better overall survival than C patients (25 alive, 30%, PV, versus 7 alive, 17%, C) and a longer median survival (24.5 months PV, versus 16 months C); estimated hazard ratio 0.6 (95% CI 0.4–0.9); stratified log rank p = 0.016. Conclusions: In a RCT, PV immunotherapy was associated with an 8.5 month improvement in median OS in men with mCRPC. These data provide evidence of prolonged anti-tumor activity, but need to be confirmed in a larger phase III study. [Table: see text]
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