Prostvac-type vaccine therapy in progressive prostate cancer after first-line therapy


A study just published in European Urology has suggested that early therapy with Prostvac-type vaccines might have value in the management of men with a rising PSA after first-line therapy.

The key details of this small, 40-patient study are provided in the abstract of the paper by DiPaolo et al. The study itself was complex because it discriminated between different types of Prostvac-type vaccine (Prostvac-F and Prostvac-V) and when they were given. However, the bottom line appears to be that:

  • Vaccines of this type seemed to lengthen PSA doubling times (from a median of 5.3 months pre-vaccine treatment to a median of 7.7 months post-vaccine treatment) in the first portion of this trial.
  • 25/40 patients (63 percent) were progression free at 6 months after registration
  • No treatment-related toxicity of Grade 4 or higher was seen to be associated with treatment.
  • 27 patients were eligible for and treated in step 2 of the trial.
  • These 27 patients were given a combination of continuing Prostvac treatment along with androgen deprivation therapy (ADT).
  • 20/27 patients (74 percent) achieved a complete response (CR) — a stable PSA — at 7 months.

We have to be cautious in how to interpret the data from this study for the very simple reason that a high percentage of patients with a rising PSA after first-line therapy would respond well to initial ADT, so it is hard to know whether the results of step 2 of the study are meaningful. Also, increasing the average PSA doubling time in the first step of this trial by just 2.4 months or 45 percent is hardly a powerful indicator that progressive disease has been stabilized. If the average PSA doubling time in that first step of the trial had gone from 5.3 months to something more like 15.3 months, one might have had greater confidence in this result.

The authors conclude only that:

A viral PSA vaccine can be administered safely in the multi-institutional cooperative group setting to patients with minimal disease volume alone and combined with androgen ablation, supporting the feasibility of future Phase III studies in this population.

This is a perfectly reasonable conclusion, but the great unanswered question is going to be, “Does this make any difference to overall, long-term survival?” That will be a much harder question to answer because it could take a trial in several hundred patients that needs 10+ years of follow-up to get a clear set of results.

Hopefully, long before we start to think about the possibility of a trial like that one, we will have the results of the trial of Prostvac-V/F in metastatic, castration-resistant prostate cancer (mCRPC). As of October 2014, that trial was still enrolling 1,200 patients.

 

2 Responses

  1. Enrollment is complete, according to a media release from Barvarian Nordic dated December 10 this year.

  2. I called on December 23 and was told, for the Illinois location, enrollment was closed.

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