Treatment for Prostate Cancer Shows Promise

[Guest guest]

By Rob Stein

An experimental treatment that harnesses the immune system to attack

tumors can extend the lives of men fighting advanced prostate cancer,

according to a study released yesterday, marking the first time a cancer

vaccine has been shown to improve survival for any malignancy.

In addition to providing badly needed hope for victims of one of the most

common cancer killers, the findings mark a watershed for the long-sought

goal of using vaccines to fight malignancies, experts said.

" We are very excited, " said J. Small of the University of California

at San Francisco, who led the study. " We think this is going to open up this

whole field. "

Other researchers agreed, saying that although the results need to be

confirmed, they should reinvigorate a strategy for treating cancer that had

been the focus of intense interest over the past decade but failed to

fulfill initial expectations.

" This is a significant development, " said L. Gulley of the National

Cancer Institute. " It is both meaningful for patients who have prostate

cancer but also for the field. It provides a proof of concept that vaccines

can in fact work, and that has generally been lacking. "

Unlike traditional vaccines, cancer vaccines are designed to treat rather

than prevent disease by stimulating the immune system to attack cancer cells

as it would invading bacteria or viruses. Although hope had dimmed for the

approach, some scientists have quietly continued to pursue it.

" It seemed really good, and then the pendulum swung back because we didn't

see promising results, but now this is clearly some of the strongest

evidence we've seen of a clinical benefit, " Gulley said.

For this vaccine treatment, doctors removed certain immune system cells

from patients with advanced prostate cancer, processed them in the

laboratory with a protein on prostate cancer cells (called prostatic acid

phosphatase, or PAP), and then injected the modified cells back into the

patients in three infusions over the course of a month. The idea is to

provoke other immune system entities known as T cells to seek out and

destroy prostate cancer cells throughout the body.

" The theory is that these [modified immune system] cells then communicate

with the T cells, which go out and do their thing and kill the prostate

cancer cells, " Small said.

In the new study, Small and his colleagues gave the vaccine to 82 men whose

cancer had progressed after surgery and radiation treatment, and a placebo

to 45 similar men. Those receiving the vaccine survived a median of 25.9

months, compared with 21.4 months for those receiving the dummy vaccine -- a

4 1/2-month difference that exceeds the benefit produced by chemotherapy.

After 36 months, 34 percent of the men receiving the treatment were alive,

compared with 11 percent of those who received the placebo.

" That's a real, significant clinical impact, " said Small, who is presenting

the findings this week at a prostate cancer symposium in Orlando that is

co-sponsored by the American Society of Clinical Oncology. Small has no

financial interest in the treatment.

The infusions can cause fever, chills and other flulike symptoms in some

patients, but no serious side effects. " It's very benign, especially

compared to chemotherapy, " Small said.

It remains unclear how long the treatment can hold the cancer in check, he

cautioned.

But the results are encouraging because there are so few options for men

with advanced prostate cancer, said Bearse of the National Prostate

Cancer Coalition.

" Whenever you have something that comes out that really kind of changes the

treatment landscape in the prostate cancer field, it's very encouraging, "

Bearse said. " It gives a lot of hope. "

More than 232,000 cases of prostate cancer are diagnosed each year in the

United States, making it the leading cancer among American men. Most men can

be treated with surgery, radiation and hormone therapy. But more than 30,000

men die each year after their cancers progress, making it second only to

lung cancer in causing deaths. There was no follow-up treatment available

until May, when the Food and Drug Administration approved the drug Taxotere

for prostate cancer.

Other experts agreed that the new findings were encouraging but cautioned

that they needed to be confirmed.

" I think they are very exciting findings, " said Philip Kantoff of the

Dana-Farber Cancer Center in Boston. " The question is whether it is real --

that's the central question. It's very provocative and needs to be

confirmed. "

Dendreon Corp. of Seattle, which is developing the vaccine, has begun a

second study of the therapy, dubbed Provenge, involving 98 men with advanced

prostate cancer. So far, the study appears to be confirming the findings,

said H. Gold, the company's president and chief executive. If the

final results hold up, the company could file for approval by the FDA by the

end of the year, he said. The company also plans to test the treatment on

men with earlier stages of prostate cancer, Gold said.

The findings suggest that scientists may have been too quick to discard

some experimental cancer vaccines when they did not appear to shrink tumors,

as was the case with Provenge, Gulley said.

" It may be these biologic agents do little in causing shrinkage of disease,

but if they generate a good enough immune response, they could continue to

benefit the patient, " he said. " This is very intriguing. "