Overall Survival of Patients With PSA-Recurrent Prostate Cancer: Long-Term Analysis of a Randomized Phase 2 Trial of pTVG-HP DNA Vaccine Versus Placebo.
Patients treated with the pTVG-HP DNA vaccine had a median overall survival of 13.4 years compared to 8.6 years for those receiving placebo, suggesting potential long-term benefits.
Where it sits
this study against the rest of the leuprorelin corpusSummary and findings
This study evaluated the long-term overall survival of patients with PSA-recurrent prostate cancer treated with the pTVG-HP DNA vaccine versus placebo. The median overall survival was reported as 13.4 years for the pTVG-HP group compared to 8.6 years for the placebo group. The findings were based on a follow-up period of 4.1 years.
Abstract
<h4>Background</h4>We previously reported results from a randomized phase 2 trial evaluating a DNA vaccine (pTVG-HP) encoding prostatic acid phosphatase (PAP) versus placebo (GM-CSF vaccine adjuvant alone) in patients with PSA-recurrent, nonmetastatic, noncastrate prostate cancer (NCT01341652). The primary endpoint of 2-year metastasis-free survival (MFS) was not different between the treatment arms. This trial was reopened for long-term evaluation.<h4>Methods and results</h4>The median follow-up for long-term overall survival was 4.1 years (range 0.1-13.8+ years). Median overall survival of 48 patients treated with pTVG-HP was 13.4 years versus 8.6 years for 49 patients treated with placebo (hazard ratio [HR] = 0.42, 95% confidence interval [CI], 0.20-0.90). Long-term follow-up information on survival and subsequent treatments was available for 59 patients treated at one site. Of these, 56 were treated with subsequent androgen deprivation therapy (ADT). When analyzing overall survival for this cohort, the adjusted HR was 0.60 (95% CI, 0.36-1.00) when comparing pTVG-HP versus placebo, after adjusting for baseline characteristics and for ADT and subsequent treatment exposure. The median time to beginning ADT was 2.2 years for patients randomized to pTVG-HP versus 1.4 years for patients randomized to placebo. The median time to the next therapy for castration-resistant disease after beginning ADT was 4.7 years for patients randomized to pTVG-HP versus 2.1 years for patients randomized to placebo.<h4>Conclusions</h4>These results suggest that pTVG-HP may have had a single-agent benefit that could not be appreciated using an MFS endpoint. This is consistent with results from other trials of anticancer vaccines, which suggest that these may have more impact on longer-term endpoints such as survival.
Background
The study addresses the long-term survival outcomes of patients with PSA-recurrent, nonmetastatic, noncastrate prostate cancer treated with a DNA vaccine. Previous reports indicated no difference in 2-year metastasis-free survival between treatment arms. This long-term analysis is important to evaluate potential benefits of the vaccine on overall survival.
Methods
This was a randomized phase 2 trial with a total of 97 patients, where 48 received the pTVG-HP vaccine and 49 received placebo. The median follow-up duration was 4.1 years, with a range of 0.1 to 13.8+ years. The primary outcome measure was overall survival, while secondary measures included time to androgen deprivation therapy (ADT) and subsequent treatments.
Results
The median overall survival for the pTVG-HP group was 13.4 years compared to 8.6 years for the placebo group, yielding a hazard ratio of 0.42 (95% CI 0.20-0.90). After adjusting for baseline characteristics and treatment exposure, the adjusted hazard ratio was 0.60 (95% CI 0.36-1.00).
Interpretation
The findings suggest a significant difference in overall survival favoring the pTVG-HP vaccine, although the clinical significance of the hazard ratios should be interpreted with caution given the small sample size and potential confounding factors. The results align with other studies indicating that anticancer vaccines may have a more pronounced effect on long-term survival rather than short-term metrics.
Key findings
- Median overall survival of 48 patients treated with pTVG-HP was 13.4 years versus 8.6 years for 49 patients treated with placebo, HR = 0.42, 95% CI 0.20-0.90.
- Adjusted HR for overall survival comparing pTVG-HP versus placebo was 0.60 (95% CI 0.36-1.00).
- Median time to beginning ADT was 2.2 years for pTVG-HP versus 1.4 years for placebo.
- Median time to next therapy for castration-resistant disease after beginning ADT was 4.7 years for pTVG-HP versus 2.1 years for placebo.
Limitations
- Small sample size (n=97).
- Single-site study, limiting generalizability.
- Median follow-up of 4.1 years may not capture long-term outcomes.
- Adjusted HR indicates potential confounding factors.