Robert Reiter, MD Robert Reiter, MD

Vaccine Therapy for Prostate Cancer?

Dendreon, a Seattle biotechnology company, released a press report claiming that the Phase 3 study of its vaccine therapy for prostate cancer was positive. This follows previous smaller studies suggesting a survival benefit for men with metastatic prostate cancer who received the vaccine.

What is this vaccine? Vaccines for cancer are different from those given to prevent measles, chicken pox and polio. They do not prevent cancer, but are intended to stimulate the immune system to combat exisiting cancers. The Dendreon vaccine is comprised of autologous dendritic cells (white blood cells taken from the patient) that are engineered to express (contain) a prostate antigen (protein) called prostate acid phosphatase and the immune stimulating protein GM-CSF. This cocktail is believed to enable the white blood cells to stimulate an immune response against prostate cancer.

Does it work? The press release claims that the vaccine prolonged the lives of men with metastatic prostate cancer when compared to men who did not receive the vaccine. We do not yet know by how much it may have prolonged life, and the detailed results are not available to examine the data critically. This information will be forthcoming.. What is odd is that the vaccine is purportedly extending life even though it has never been shown to reduce PSA levels or even stabilize them. It has not been shown to delay the progression or advancement of disease. Therefore, it is still not understood how or why one might get a prolongation of life without having any effect on any other measure of the disease. Is life extended without any improvement in quality of life? These are all question that must be answered.

The upshot? We need to wait for the results to be reported and scrutinized. The FDA must approve the vaccine. The vaccine will be very expensive because it must be manufactured on an individual by individual  basis, and there is some concern whether this is feasible on a large scale. So only time will tell if we really have the first active vaccine for a solid tumor. In the meantime, there are a host of promising drugs out there for advanced prostate cancer about which I and others are very very optimistic. At UCLA right now, we have trials for the exciting drug Abiraterone, among others.

04:00 PM, 15 Apr 2009 by Rob Reiter Permalink | Comments (0)



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