Soy extract and prostate cancer link
prostate-specific antigen levels by as much as 61 per cent in a
group of prostate cancer patients undergoing 'watchful waiting' for
their disease, report US researchers.
A dietary supplement containing the soy extract genistein reduced prostate-specific antigen (PSA) levels by as much as 61 per cent in a group of prostate cancer patients undergoing 'watchful waiting' for their disease, report researchers at the University of California (UC) Davis Cancer Center.
The news comes on the heels of the news on Friday that the UK's independent scientific Committee on Toxicity (COT) is urging the UK government to review its advice on the use of soya-based infant formulas, following a new report suggesting that there is a lack of evidence on phytoestrogens and health.
Genistein is described as one of two compounds in soy that belong to a family of chemicals known as isoflavones. Isoflavones are phytoestrogens, plant-based chemicals that mimic the effects of oestrogen in the body. The authors mention that genistein concentrated polysaccharide has been widely used as a complementary therapy for various cancers in Japan, Korea and other parts of Asia.
Meanwhile PSA is a blood marker for prostate cancer. The researchers explain how an increase in PSA is a warning sign of prostate cancer, thus elevated PSA levels in men who have been treated for prostate cancer may signal a recurrence or progression of the disease.
While effective in some, the dietary supplement did not have the same effect in men who had undergone surgery, radiation or hormone therapy for their prostate cancer. "This study must be interpreted cautiously because the numbers of men enrolled are small," emphasised Ralph deVere White, professor and chair of urology at UC Davis School of Medicine and Medical Center and director of the UC Davis Cancer Center.
"However, the findings do stimulate us to do a larger, placebo-controlled trial in patients who are on watchful waiting." Watchful waiting is recommended for some men whose cancer is causing no symptoms, is expected to grow very slowly, and is small and contained within one area of the prostate.
In the study, 62 men with biopsy-proven prostate cancer and elevated PSA levels were given 5 grams a day of genistein concentrated polysaccharide for six months. Sixteen of the men were on watchful waiting for their disease. The remaining 46 had undergone surgery, radiation or hormone therapy.
Of those 46 men, one had no change in his PSA level during the study; the rest all had increases in PSA.
Among the 16 men on watchful waiting, three stopped therapy due to diarrhoea. Of the 13 who completed the study, eight saw a drop in their PSA level, with the decreases in PSA ranging from 3 per cent to 61 per cent.
In total five of the 13 watchful waiting patients who completed the study, or 38 per cent, had increased PSA levels over the course of the study, compared with 98 per cent of the men with treated prostate cancer.
"Patients on watchful waiting may do better due to grade of disease or distribution and concentration of genistein within the prostate," the study authors suggest, adding that "further research is needed to determine this".
The UC Davis study was supported by genistein supplement manufacturer Amino Up Chemical of Sapporo, Japan, and was reported on 30 May at the 2003 meeting of the American Urological Association meeting in the US.
