A well-known herbal treatment for advanced prostate cancer, PC-SPES, has been found to be altered with manufactured drugs, and has been taken off the market.

Researchers from California and the Czech Republic found that PC-SPES, contained diethylstilbestrol (DES), which is a synthetic estrogen; indomethacin, a potent anti-inflammatory drug; and warfarin, a powerful anticoagulant (blood thinner). They reported their findings at the April meetings of the American Association for Cancer Research in San Francisco.

PC-SPES is said to be an herbal extract of several natural plant substances. It is manufactured in China and distributed in the US by a single firm.

The researchers' findings verified what many had long suspected — that this supplement was effective not because it contained active herbal extracts, but because it contained a form of the female hormone, estrogen.

One of the researchers, Robert Nagourney, MD, of Long Beach, Calif., had been treating his advanced prostate cancer patients with PC-SPES for several years. Although he was impressed with the success of the treatment, he was puzzled by the side effects. The men would complain of breast tenderness and enlargement.

Other investigators had reported the same thing. PC-SPES was effective in treating advance prostate cancer, but the men's breasts would enlarge. The investigators found that the herbal drug acted like estrogen in other ways as well. Doctors reported that their patients were often developing blood clots, a well-known side effect of estrogen treatment.

Then in 2001, doctors from Seattle reported a man taking PC-SPES, who started bleeding excessively. The Seattle doctors found that he had warfarin in his blood, a commonly used blood thinner.

Most doctors felt that the herbs were causing the estrogen effects, but the anticoagulant effect couldn't be readily explained. Also, Nagourney found that PC-SPES would kill cancer cells in test tubes, something herbal extracts wouldn't do but estrogens could.

This led to the group of researchers combining their talents and performing very sophisticated chemical tests of PC-SPES. What they found was that until 1999, multiple lots of PC-SPES contained large amounts of DES and indomethacin. After 1999, the levels of these drugs declined, but warfarin appeared in the PC-SPES lots.

The researchers think the US distributor knew nothing about this contamination. They suspect that the Chinese manufacturers were adding the compounds before shipping to the US. These were not just contaminants of the herbal extraction process, because DES, indomethacin, and warfarin are chemicals not found in nature.

The Chinese added the DES because they knew it was a good treatment for prostate cancer, and they added the other ingredients (indomethacin is not only a pain killer, it also prevents clotting) to help prevent the blood clots that often accompany DES treatment.

Because of the inclusion of manufactured drugs, the US distributor has taken PC-SPES off the market. What is the future of PC-SPES?

"I think it will disappear," said Nagourney. But he pointed out a bright spot. It brings to our attention the value of an old discarded treatment for advanced prostate cancer — DES.

"I'm using it [DES] now," said Nagourney, who believes it may work better than many of the newer hormone treatments for advanced prostate cancer.