Previous research suggests the extract can stabilize or reverse some cancers
Men who are on active surveillance or “watchful waiting� for prostate cancer may be eligible to enroll in a UC Davis Cancer Center clinical trial of genistein concentrated polysaccharide, or GCP, a food extract derived from soybeans and shiitake mushrooms. The new study builds on a preliminary trial, completed last year, that found GCP reduced levels of prostate-specific antigen in a small group of “watchful waiting� patients.
Watchful waiting is recommended for some prostate cancers that cause no symptoms, are expected to grow very slowly, and are small and contained within one area of the prostate. Prostate-specific antigen, or PSA, is a protein that serves as a marker for prostate cancer. Rising blood levels of the protein in men with diagnosed prostate cancer can be a signal of disease progression, while falling levels can signal remission. GCP is used as a complementary therapy for prostate cancer in Japan, Korea and other parts of Asia.
“If we can find a chemopreventive agent capable of slowing or stopping the progression of early, localized prostate cancer, we’ll have something to offer men besides watchful waiting,� said Ralph deVere White, professor and chair of urology at UC Davis School of Medicine and Medical Center, director of the UC Davis Cancer Center and a principal investigator of the GCP trial. “It would be an important development in prostate cancer.�
DeVere White conducted a preliminary clinical trial of GCP in men with prostate cancer last year. Published in the February issue of the journal Urology, the study found that PSA levels stabilized or dropped in eight of 13 “watchful waiting� patients who took GCP. However, GCP did not improve PSA levels in study subjects who had received surgery, radiation or hormone therapy for their cancers, perhaps because their disease was more advanced or aggressive, or because the medical treatments reduced GCP concentrations within the prostate.
In the new trial, UC Davis researchers will investigate the effects of GCP only in prostate cancer patients on watchful waiting. To be eligible to participate, volunteers must have biopsy-proven prostate cancer and have undergone no previous treatment for the cancer. In addition, patients must have decided, in consultation with their doctors, to continue to receive no treatment for their cancer for the next six months. Potential participants also must have a PSA level of 2 nanograms per milliliter of blood or higher; participants whose PSA is above 10 must have been on watchful waiting for at least one year.
During the six-month trial, participants will be randomized to receive either GCP or placebo capsules. Neither the patients nor the study investigators will know who is taking the placebo until the end of the six-month period. At the end of the trial, patients who received the placebo, along with patients who received GCP but had minimal change in their PSAs, will be offered a six-month supply of the supplement. At the end of that six-month period, all patients who continue to show a decreased or stable PSA may continue receiving GCP at no cost, as long as they have their PSAs checked every six months.
Participants will visit UC Davis Cancer Center three times during the six-month study to have their blood drawn for PSA testing and other analyses, and to be monitored for evidence of side effects. Side effects may include gastrointestinal symptoms, such as diarrhea.
People who have an allergy to soy or soy products, who are already taking more than 2 grams of genistein a day in nutritional supplements or who have participated in a previous GCP clinical trial at UC Davis are not eligible for the study.
The study is sponsored by Amino Up Chemical Co., Ltd., of Sapporo, Japan, a GCP manufacturer.
UC Davis Cancer Center is the only National Cancer Institute-designated cancer center between San Francisco and Portland, Ore. Its Integrated Cancer Research Program with Lawrence Livermore National Laboratory, the nation’s first such partnership between a major cancer research center and a national laboratory, coordinates the efforts of more than 200 scientists on the UC Davis Medical Center campus in Sacramento, the UC Davis campus in Davis, and at the national laboratory in Livermore, Calif. The program includes cancer investigators from the the UC Davis College of Agricultural and Environmental Sciences, the UC Davis School of Veterinary Medicine and the UC Davis College of Engineering, among other departments, programs and centers.