New Vaccine Developed to Stop Prostate Cancer Recurrence

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For those patients diagnosed with localized prostate cancer, the risk of recurrence is approximately 30%, even a year after initial treatment. 

But now, researchers at the U.S. National Cancer Institute are testing 70 men who've already had prostate cancer and are seeing an increase in their PSA, with a newly developed vaccine designed to halt prostate cancer from recurring. 

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Who Developed the Vaccine

Advantagene, a biotech company based in Newton, Mass., has designed a prostate cancer vaccine known as ProstAtak. Unlike traditional vaccines that attempt to prevent disease, ProstAtak is designed to prevent recurrence. 

This vaccine works via a gene transfer method by administering a series of three injections (ProstAtak or placebo) directly into the prostate--followed by 14 days of valacyclovir pills. The hope is that the ProstAtak vaccine will rev up the body's immune system, which in turn will detect and destroy recurring cancer cells.

Injections are performed using transrectal-guided ultrasound (TRUS), the same method used to perform a prostate biopsy. This procedure is performed in conjunction with standard radiation treatment.

How the Prostate Cancer Vaccine Works

The vaccine is made from a protein called TARP, which is found in 95% of prostate cancers. Previous animal studies have shown this protein can teach the immune system to attack cancer cells. It's designed to teach the immune system to recognize compounds found in prostate cancer cells and is currently being given to men who have already been treated for the disease. 

The thinking is that the vaccine will prime the immune system so that it creates antibodies when it detects TARP-related cancers.

Then, should the cancer reappear, the antibodies will be dispatched to attack the malignant cells. Those antibodies, along with other immune cells, can then destroy cancer cells without harming non-cancer cells, so minimizing side-effects.

It is initially being tested as a way to treat cancer that has returned but, if successful, could be experts predict it could be used as a first line of treatment for prostate and potentially breast cancer in the future. TARP is also found in about 50% of breast cancers.

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Watchful Waiting and Prostate Cancer Recurrence

Once they have been treated, men are monitored with regular blood tests that check for a protein called prostate specific antigen or PSA, which can indicate cancer. The time it takes for the PSA reading to double is called the PSADT. Men with a PSADT of less than three months are at high risk of dying from prostate cancer. 

Men in the vaccine's initial trial will have a PSADT greater than three months and less than 15. The trial will last nearly two years, and men will be given six injections of the vaccine or a placebo during that time.