Vaccine Offers Hope to Men With Metastatic Prostate Cancer

Stephanie Doyle

May 22, 2008

May 22, 2008 (Orlando, Florida) — A new prostate cancer vaccine could give hope to men with metastatic prostate cancer by enabling their immune systems to fight the disease.

Researchers from the University of Iowa presented data on the adenovirus/prostate-specific antigen (Ad/PSA) vaccine here at the American Urological Association 2008 Annual Meeting.

"The initial early indication [of this new prostate cancer vaccine] is that safe and has some efficacy — I think it is one of the most exciting cases [presented] at the meeting," said Ira D. Sharlip, MD, clinical professor of urology at the University of California, San Francisco, who was not involved in the study.

In recent years, the concept of vaccine immunotherapy for advanced prostate cancer has become increasingly highlighted as research has increased. Major advances in the field have contributed significantly to the discussion of this cancer therapy as researchers explore new ways to prolong survival and improve the quality of life of patients with metastatic disease.

PSA is a protein produced by the cells of the prostate gland. Rising levels of PSA over time are associated with both localized and metastatic prostate cancer. The goal of immunotherapy for metastatic disease is to manipulate the body's immune system so that it can identify and destroy cancer cells.

The Ad/PSA vaccine was developed by inserting the PSA gene into bacteria and viruses and using immune-stimulatory deoxyribonucleic acid (DNA) to modulate the body's antitumor response. Enabling a patient's immune system to produce antiantigens and attack cancer cells can improve quality of life and extend survival. Earlier studies in mice demonstrated the vaccine's efficacy; it produced strong anti-PSA and, as a result, powerful antiprostate cancer immunity.

This phase 1 clinical trial assessed the performance of the Ad/PSA vaccine in men with measurable metastatic prostate cancer. The 32 eligible patients with stage D2 or D3 cancers (median age, 71 years; median PSA, 128 ng/mL) were treated with 1 of 3 dose levels of the vaccine (106, 107, or 108 pfu/mL).

The patients were followed with physical and clinical chemistry exams at 2 and 3 weeks and at 2, 4, 8, and 12 months. The median follow-up was 12 months and median survival was 18 months.

After receiving the vaccine, at least 40% of patients developed immune responses to PSA, with anti-PSA antibodies produced in 42% of patients and anti-PSA T-cell responses in 71%. In all, 57% of patients survived longer than predicted, and doubling time increased in 48%. The longest survival was 71 months — nearly 6 years.

Researchers are now recruiting 82 patients for a phase 2 clinical trial, which recently was approved by the US Food and Drug Administration. The estimated study completion date is December 2010.

This study "encouraged us enough to generate our grant application and protocol for phase 2,'' David M. Lubaroff, MD, told Medscape Urology. Dr. Lubaroff, principal investigator of the phase 1 study, is professor of urology and microbiology and associate director of the Holden Comprehensive Cancer Center at the University of Iowa, in Iowa City. "We're excited by the results of phase I and are cautiously optimistic," he said.

Funding was provided by the University of Iowa's College of Medicine and Cancer Center. The authors disclosed no relevant financial relationships.

American Urological Association (AUA) 2008 Annual Meeting: Abstract 526. Presented May 18, 2008.


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