The supplement, called PC-SPES, merits further study as a possible agent to slow the disease and delay the need for chemotherapy in patients who aren''t responding to hormone treatment, says lead author Eric J. Small, MD, associate professor of medicine and urology at the University of California at San Francisco.

PC-SPES appears to work in "hormone-resistant" or "hormone-independent" patients for whom anti-androgen hormones failed to reduce PSA levels, Small says. PSA is a protein produced by prostate tissue and prostate cancers, and monitoring its levels in the blood is a common method of assessing the usefulness of prostate cancer treatments. Fifty-four percent of men with hormone-resistant prostate cancer had a drop in PSA levels of at least 50% after taking PC-SPES. Some even had measurable improvement in size of metastases seen on bone scans.

"PC-SPES gives us a new weapon in an area where hormones don?t always work," Small says. "Do I see it as a cure for prostate cancer? No. But it can put off chemotherapy." For patients who do respond to the commonly used hormone therapies, PC-SPES seems to offer no advantages, he says.

One goal of the study was to document the side effects and toxicity of PC-SPES, which had never been done despite its widespread use. As a supplement rather than a drug, PC-SPES is not required to undergo FDA approval.

The side effects included breast enlargement and tenderness (97% of patients), hot flashes (42 %), and decreased libido (100%), according to the article. The supplement was relatively well-tolerated by the patients in the study, except for a few cases (4%) of thromboembolism, in which a piece of a blood clot breaks free and clogs a blood vessel. But the researchers say this was a minor risk. That risk might be prevented if further studies look at combining PC-SPES with drugs that would prevent thromboembolism.

For now, Small says he cannot recommend using PC-SPES in combination with other drugs until more is known about potential interactions.

"It''s a fairly complex mixture with multiple components, and the potential for many side effects," he says.

PC-SPES is a combination of extracts from eight Chinese herbs. It is marketed simply for "prostate health," Small says. The manufacturer is Botanic Labs of Brea, Calif., which sold the capsules at cost for the study, according to the article.

A clinical trial for such alternative and complementary preparations is rare, Small adds. "What we encountered were two reactions [to such potential therapies]: either outright rejection without any clinical trials just because they''re alternative, or outright acceptance without clinical facts, simply because they''re alternative," Small said.

"We wanted to hold this compound to the same standards as any new agent," he says.

"This is exciting, and it raises a number of other possibilities," says David S. Rosenthal, MD, medical director of the Zakim Center for Integrative Medicine at the Dana Farber Cancer Institute, and former president of the American Cancer Society (ACS).

The scientific community and funding organizations are turning more attention to clinical trials of alternative and complementary cancer therapies, Rosenthal says. He and other researchers are also looking at what effect phytoestrogens, which are present in soy, might have on prostate cancer.

"This has been pushed by patients," Rosenthal says. "I think the medical profession has been a little slow to catch up."

The next step in Small''s study is already underway at the UCSF Comprehensive Cancer Center and at the Dana Farber Cancer Institute in Boston. In a group of 108 men with prostate cancer, half the men will take PC-SPES, and half will take estrogen, for as long as those respective agents seem to reduce PSA levels, Small says. But as soon as the effect stops, the participant will switch from one preparation to the other, to see if that makes a difference.

If the estrogen stops working for a participant, but switching to PC-SPES causes his PSA levels to drop again, that would indicate PC-SPES offers an additional advantage, Small says.