Overall Survival Benefit With Prostate Cancer Vaccine Not Duplicated in Phase 3 Trial
Prostvac-V/F consists of a recombinant vaccinia vector as a primary vaccination, followed by booster doses with a recombinant fowlpox vector.
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Prostvac-V/F, an investigational prostate cancer (PCa) vaccine regimen, does not improve overall survival among men with asymptomatic or minimally symptomatic metastatic castration-resistant prostate cancer (mCRPC), according to the findings of the phase 3 PROSPECT trial presented at the 2018 American Society of Clinical Oncology Annual Meeting in Chicago, Illinois.1
The latest findings failed to confirm an overall survival (OS) benefit found in a previous randomized phase 2 trial (RandPh2). In that earlier trial, median OS was significant greater among Prostvac-treated patients than placebo recipients (25.1 vs 16.6 months). Prostvac-V/F consists of a recombinant vaccinia vector as a primary vaccination, followed by 6 booster doses with a recombinant fowlpox vector.
In the PROSPECT trial, James L. Gulley, MD, of the National Cancer Institute in Bethesda, Maryland, and colleagues, randomly assigned 1297 men from 15 countries to receive either Prostvac-V/F plus placebo, Prostvac-V/F plus GM-CSF (granulocyte-macrophage colony-stimulating factor), or placebo plus placebo. Median OS for the groups was 34.8, 33.9, and 34.7 months, respectively. The differences between the Prostvac-V/F-placebo and placebo-placebo groups and Prostvac-V/F-GM-CSF and placebo-placebo groups did not differ significantly (HR 1.02; P = .40 and HR 1.03; P = .66, respectively).
Dr Gulley's group noted in their study abstract that the OS observed in all study arms was about 1 year longer than anticipated based on historical controls, “likely related to improved standard of care since study enrollment began in 2011.”
Adverse events of any grade occurred in 91% of patients, and 65% had injection site reactions, but only 5.8% led to premature discontinuation of treatment, according to the investigators.
The study population had a mean age of 71 years and mean PSA level of 74.5 ng/mL. Bone, lymph node, and visceral metastases were present in 74.7%, 15.7%, and 8.4% of patients, respectively.
Gulley JL, Borre M, Vogelzang NJ, et al. Results of PROSPECT: A randomized phase 3 trial of PROSTVAC-VF (PRO) in men with asymptomatic or minimally symptomatic metastatic, castration-resistant prostate cancer. J Clin Oncol. 2018: 36, (suppl; abstr 5006). Presented at 2018 ASCO Annual Meeting; June 1-5, 2018; Chicago, IL.