New Treatment Options on Horizon for Early Relapse Prostate Cancer Patients

Vaccine therapy stimulates immune defenses.

Investigators are evaluating a new treatment for prostate cancer patients who suffer from early relapse by utilizing the body’s own immune defenses to fight the disease.

In a study published in the current online edition of European Urology, researchers evaluated adult patients with hormone therapy resistant advanced prostate cancer, as evidenced by rising protein-specific (PSA) values with no visible metastasis.

The phase 2 clinical trial examined 2 different experimental treatment options developed from viruses.

PROSTVAC-V is derived from a vaccinia virus used to vaccinate against smallpox, which is modified to yield a PSA protein that helps focus the immune response to the PSA in the prostate tumor. Additionally, the treatment is modified to produce 3 other proteins that increase an immune cell's ability to destroy its target (TRICOM).

PROSTVAC-F is made from the fowlpox virus found in birds, which is not known to cause any diseases in humans. The treatment contains the same genetic material as PROSTAC-V, but is administered multiple times to further boost the immune system.

Patients were given 1 cycle of PROSTVAC-V/TRICOM followed by PROSTVAC-F/TRICOM for subsequent cycles in combination with a drug called GM-CSF, which is a protein made by the body to increase and make more active the amount of certain white blood cells. In drug form, GM-CSF enhances the body's immune system to fight disease.

After 6 months from baseline, 25 of 40 eligible patients had no disease progression with minimal toxicity. The median pre-treatment PSA velocity was 0.13 log (PSA)/month, compared with a median post-registration (6 months) velocity of 0.09 log (PSA)/month. This represents an improved PSA doubling time, going from 5.3 months to 7.7 months.

The second part of the study involved adding hormone therapy androgen ablation to the PROSTVAC-VF/TRICOM combination. In 27 eligible patients, 20 patients experienced a complete response at 7 months.

"Previous studies by the ECOG-ACRIN Cancer Research Group and others have shown it is optimal to explore agents like PROSTVAC that harness the body's own defenses in shutting down cancer,” said lead author Robert S. DiPaola, MD, in a press release. “With our current findings demonstrating the safe use of combination vaccine therapy earlier in the course of prostate cancer progression, we are laying the groundwork for future immunotherapy options for this patient population.”