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.

BACKGROUND

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.

METHODS AND

RESULTS

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.

CONCLUSIONS

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.