Journal of Clinical Oncology, 2005 ASCO Annual Meeting Proceedings.
Vol 23, No 16S (June 1 Supplement), 2005: 2504
© 2005 American Society of Clinical Oncology

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Abstract

A phase II study of PROSTVAC-VF vaccine, and the role o f GM-CSF, in patients (pts) with metastatic androgen insensitive prostate cancer (AIPC)

National Cancer Institute, National Insts of Health, Bethesda, MD

2504

Background: Vaccine strategies represent a novel therapeutic approach for the treatment of metastatic AIPC. Preclinical and clinical studies have demonstrated that the induction of T-cell responses directed against a PSA can lead to anti-tumor activity in the absence of toxicity. Two novel PSA-based vaccines have been developed: (a) a recombinant (r) vaccinia virus containing the entire PSA transgene with a modified agonist epitope and three costimulatory molecule transgenes, rV-PSA-TRICOM (rV) and (b) a similar recombinant fowlpox virus, rF-PSA-TRICOM (rF). We have completed a phase I study demonstrating the clinical safety of a prime/boost vaccine strategy: priming with rV with subsequent monthly boosts using rF. Methods: This phase II study randomizes 32 pts with metastatic AIPC without prior chemotherapy and progressive disease into one of the following 4 cohorts utilizing the same vaccine used in the phase I study. Pts randomized to cohort 1 receive vaccine alone, pts in cohort 2 receive vaccine with recombinant GM-CSF protein, and pts in cohorts 3 and 4 receive vaccine with 2 different doses of fowlpox-GM-CSF. Pts receive restaging scans every 3 months while on study and may continue to receive vaccine until disease progression. Results: To date, 25 pts have enrolled on study and 16 have undergone restaging evaluation at 3 months. Five of these pts have demonstrated PSA declines during this period, 4 pts with PSA declines of >30% and 1 pt with a decline of >50%. Eleven of 23 pts continue on treatment with 6 of 20 pts continuing on study beyond the initial 3-month period. One patient at 8 months has experienced a PR by RECIST criteria with >50% decrease in unidimensional measurement of his hilar adenopathy. Another pt who remains with stable disease after 10 months of treatment has had a 29% decrease in his soft tissue disease. A third pt on study for 11 months continues to have stable disease. Immunologic studies are planned to monitor pts immune responses measuring changes in PSA specific T cells. Conclusions: This vaccine can be given safely and has been associated with declines in PSA in several pts with one pt having an impressive decrease in his soft tissue lesion.

No significant financial relationships to disclose.

Abstract presentation from the 2005 ASCO Annual Meeting