The Study: If only it did. Sipuleucel-T, a therapeutic vaccine to prostatic acid phosphatase, was approved for use in men with metastatic castration-resistant prostate cancer (mCRPC) after multiple randomized trials showed improved overall survival—conspicuously minus an improvement in progression-free survival. PROSTVAC, similar in concept, is a PSA vaccine that uses two poxvirus-based vectors. Based on the results of a phase 2 trial showing improved survival, this phase 3 trial randomized men with chemo-naive mCRPC newly-progressed on anti-androgen therapy to  PROSTVAC +/- GM-CSF or  just placebo. Sadly, there was no difference in the median overall survival between groups at 33-34 months nor was there a difference in the rate of events at 6 months, 60% of which were radiographic only. There was quite a bit of hand-wringing in the discussion that ultimately gets at the unfortunate fact that PROSTVAC, as opposed to sipuleucel-T, entered a crowded market for mCRPC treatments and simply provided no evidence of additional clinical benefit in this population.
Bottom Line: The PSA vaccine PROSTVAC failed to improve overall survival or reduce progression in men with mCRPC. | Gulley, J Clin Oncol 2019