Monday June 22 2009
Men were given a tablet containing green tea extract
“A chemical found in green tea appears to slow the progression of prostate cancer,” BBC News has reported. According to its website, previous studies have shown that drinking green tea has health benefits, including some positive findings related to prostate cancer.
The news comes from the results of a small trial, in which men with prostate cancer were given daily doses of pills containing polyphenols, a class of chemicals found in green tea. Taking the Polyphenon E capsule led to a significant reduction in the blood levels of certain chemicals that are considered to be markers of the severity of the disease. The authors suggest that this change in chemical levels may reflect a slowing down of the progression of disease.
However, an actual slowing of the disease’s progression has yet to be proven as this study did not assess clinical outcomes of the patients but only changes in the levels of these chemicals. The changes were modest in some cases and the researchers call for further studies into the effects of green tea extracts. This initial study is likely to be followed by a larger trial, in which patients are randomly assigned to receive either Polyphenon E or a placebo dummy pill. The results from larger, more robust study designs should hopefully prove more conclusive.
Where did the story come from?
Dr Jerry McLarty and colleagues from Louisiana State University Health Sciences Center and Overton Brooks VA Medical Center, Louisiana, carried out this study. The research was funded by the Polyphenon Pharma pharmaceutical company, which supplied the drug used in this trial. The study was published in the peer-reviewed medical journal Cancer Prevention Research.
What kind of scientific study was this?
This was an open-label trial which assessed the effect of the Polyphenon E pill in 26 men with prostate cancer who were scheduled to undergo a radical prostatectomy (surgery to remove the prostate gland).
Polyphenon E is a capsule that contains polyphenols (catechins), a family of chemicals which are naturally found in green tea. The researchers say that they may have potential as a cancer therapy.
Previous research has shown that high levels of tea polyphenols in urine were associated with an improved prognosis of breast cancer and a reduced risk of gastric cancer in people drinking five or more cups of green tea a day. Green tea consumption has also been linked to a reduced risk of lung cancer and prostate cancer. However, overall data on the subject is inconclusive as some studies found no effect on cancer risk.
The Polyphenon E pill contains a number of different polyphenols, but the researchers have previously shown that two of them (known as EGCG and ECG) have an effect on breast and prostate cancer cells in vitro (in the laboratory), inhibiting a particular biochemical pathway (the HGF/c-Met pathway) that is associated with disease severity.
In this new experiment, the researchers investigated whether taking Polyphenon E orally would reduce the blood and tissue levels of a number of specific ‘biomarkers’ (chemicals that indicate the severity of the disease). These biomarkers were hepatocyte growth factor (HGF), prostate-specific antigen (PSA), vascular endothelial growth factor (VEGF), insulin-like growth factor (IGF-I) and IGF binding protein-3 (IGFBP-3).
In this study, men were asked to take a daily dose of four capsules along with a meal. Each pill contained 200mg of Polyphenon E. The safety of the drug was monitored through liver function tests. Blood samples were taken before the study began and before prostate surgery, with a positive response defined as a 50% or greater change in tissue biomarkers. The length of treatment with Polyphenon E varied because participants were only treated during the period between their prostate biopsy and prostate surgery (an average of 34.5 days).
What were the results of the study?
The study found that levels of the biomarkers HGF, VEGF, PSA, IGF-I and IGFBP-3 (which may be indicators of prostate cancer severity) reduced significantly during the study.
What interpretations did the researchers draw from these results?
The researchers concluded that their results show a significant reduction in serum levels of chemicals that indicate the severity of the disease. This was not accompanied by an increase in liver enzymes, which would have indicated toxicity of the drug. They say that the findings support a “potential role for Polyphenon E in the treatment or prevention of prostate cancer”.
What does the NHS Knowledge Service make of this study?
This small open-label study has found that Polyphenon E had an effect on the serum levels of various chemicals that indicate the severity of prostate cancer. Average concentrations of HGF, VEGF, PSA, IGF-I and IGFBP-3 all reduced significantly in the period between the two blood tests.
When analysing their data, the researchers took into account some of the factors, including age, race and length of treatment, which may have been linked to the reductions in biomarker chemicals. These factors did not have an effect on changes in these biomarkers.
Overall, it is difficult to interpret the clinical significance of the reductions in biomarkers. As the researchers point out, it is possible that even small reductions in HGF levels could indicate a large biological effect on prostate cancer progression. However, this study did not assess the clinical outcomes of patients, only the changes in their biomarker levels.
Rightly, the researchers say that “additional longer-term studies will be needed to determine if lowering VEGF and HGF serum levels actually translates into more favourable clinical outcome.”
The authors note that, in particular, there was only a modest change in PSA levels (average change of 1.12ng/ml), which they say should be interpreted with caution. PSA levels can change for reasons that are not related to cancer progression. Similarly, the relationship between serum levels of IGF-I and IGFBP-3 and prostate cancer is unclear. A further limitation of this study is that it did not have a control group, meaning it could not establish the effects of Polyphenon E in relation to the natural chemical fluctuations that may occur without polyphenol intake.
Large, randomised controlled studies (phase III trials) are the likely next step for the study of this green tea extract. The researchers say that their findings should be verified by larger, placebo-controlled clinical trials and note that the effects of different doses, long-term administration and combination with other drugs remain to be seen.