A phase 3 trial will now determine whether PROSTVAC alone or in combination with GM-CSF is effective in prolonging overall survival (OS) in men with few or no symptoms from metastatic, castration-resistant prostate cancer (mCRPC). Its enrollment target of 1,200 asymptomatic or minimally symptomatic patients with mCRPC was completed in December 2014.
Mark Garzotto, MD, an Associate Professor of Urology and Radiation Medicine at Oregon Health & Science University in Portland, OR, said this is a very important area of research. He said it is well recognized that immune-based approaches have the potential for a very meaningful benefit in prostate cancer.
“What are needed are safe and effective regimens that can be practically administered such as this one. If this does pan out, then it could help tens of thousands of patients a year who have aggressive but early stage prostate cancer,” Dr. Garzotto told Cancer Therapy Advisor.
He noted that this trial has significant limitations, lacking a control arm and the relying entirely on PSA as the primary marker of benefit. Dr. Garzotto said before achieving U.S. Food and Drug Administration approval it will likely have to show solid clinical benefit, such as a reduction in the rates of metastases or a delay in treatment with more toxic therapies.
Kevin Courtney, MD, an Assistant Professor of Internal Medicine at the University of Texas Southwestern Medical Center in Dallas, TX, said this new vaccine approach shows promise for the treatment of prostatic adenocarcinoma and warrants further investigation.
However, he said it is important that these types of vaccines are tested in men who are receiving concomitant ADT.
“It is a well-designed study that demonstrates the safety and tolerability of this treatment in men with biochemical recurrence following local treatment for prostate cancer. The data from this single arm phase II trial support pursuing further investigation of the use of PROSTVAC-V/F/TRICOM in combination with ADT in a large, randomized controlled study,” Dr. Courtney said.
This new vaccine approach is significantly different than sipuleucel-T (PROVENGE). It would not involve individualized tailored therapy and could add to the armamentarium.
“I think it would be premature to draw conclusions at this point regarding the potential cost relative to sipuleucel-T. While the currently approved protocol for sipuleucel-T administration involves 3 leukapheresis procedures and 3 infusions of the activated dendritic cells that comprise the sipuleucel-T product, treatment with PROSTVAC-V/F/TRICOM under the protocol employed in the phase II study involved indefinite administration of the PROSTVAC-F/TRICOM along with concomitant GMCSF until progression,” Dr. Courtney told Cancer Therapy Advisor.
- DiPaola RS, Chen YH, Bubley GJ, et al.A National Multicenter Phase 2 Study of Prostate-specific Antigen (PSA) Pox Virus Vaccine with Sequential Androgen Ablation Therapy in Patients with PSA Progression: ECOG 9802. Eur Urol. December 18, 2014. [Epub ahead of print] doi: 10.1016/j.eururo.2014.12.010.