After study participants consumed 6 cups of green tea daily for 2 months, serum prostate-specific antigen (PSA) levels were significantly lower than they were at study entry (P < .01), as was the expression of PSA protein in prostate tissue (P = .06). In addition, changes in other biomarkers were observed.
"Our study showed that drinking 6 cups of green tea affected biomarkers in prostate tissue at the time of surgery," said study author Susanne M. Henning, PhD, RD, adjunct professor at the David Geffen School of Medicine at the University of California, Los Angeles. "This research offers new insight into the mechanisms by which green tea consumption may reduce the risk for prostate cancer by opposing processes such as inflammation, which are associated with prostate cancer growth," she explained.
She was speaking at a press briefing held in advance of the 11th Annual American Association for Cancer Research International Conference on Frontiers in Cancer Prevention Research, being held in Anaheim, California.
In vitro and other experimental studies have demonstrated the protective effect of green tea against some cancers. Results from epidemiologic studies have been inconclusive about the relation between green tea and prostate cancer, Dr. Henning noted.
However, in an Italian study, green tea catechins reduced the risk for progression to prostate cancer with no significant adverse effects (Cancer Res. 2006;66;1234-1240), she explained.
"Green tea is very high in polyphenols, is convenient, is widely available, and there are already data available from intervention studies," she said.
Changes in PSA and Biomarkers
In this phase 2 study, Dr. Henning and colleagues evaluated the anticarcinogenic effects of green tea in prostate cancer patients prior to surgery.
Of the 67 men who completed the study, 34 were randomized to 6 cups of brewed green tea daily and 33 were randomized to water daily for 3 to 8 weeks before prostatectomy.
Serum PSA concentration, prostate tissue PSA protein level, and prostate concentration of green tea polyphenols and their metabolites were measured. In addition, the effect of green tea on oxidative and inflammatory biomarkers, including protein expression of Ki67 (proliferation), Bcl2, Bax (apoptosis), and nuclear factor kappa B (NFκB) (inflammation), was evaluated.
Bioactive green tea catechins, which include epigallocatechin gallate (EGCG) and its methyl metabolite 4′-O-methyl-EGCG and epicatechin gallate, were detected in the prostate tissue of 31 of 34 men in the green tea group.
In the green tea group, immunostaining showed that intranuclear NFκB significantly declined, but there was no change in cytoplasmic NFκB staining in prostate tumors. The ratio of cytoplasmic staining of proapoptotic Bax to Bcl-2 was significantly higher in the green tea group, but cytoplasmic Bcl2 and Bax staining did not change. There was also no change in nuclear Ki67 staining.
In the control group, there were no changes in PSA levels.
"This is a proof-of-principle study.... The polyphenols are reaching the prostate," Dr. Henning explained. However, in this small, short-term study, no inhibition of tumor growth was seen. "Longer-term studies are needed in the prevention setting," she said.
No Recommendations Just Yet
On the basis of these data, can any recommendations be made about green tea? Not yet, according to Ernest Hawke, MD, vice president and head of the division of cancer prevention and population sciences at the University of Texas M.D. Anderson Cancer Center in Houston.
"This was only a phase 2 trial, so its intentions were pretty limited," he told Medscape Medical News. "It was mainly to figure out if the green tea polyphenols got into the prostate and, if so, what effect they had. That's all that was demonstrated here," he noted.
Dr. Hawk, who was not involved in the study, emphasized that this is a good study because "it defines a dose that can be moved into a definitive larger trial."
The study was conducted in patients with cancer, so it does not establish whether green tea can keep cancer from developing in those at risk, he added.
"To make claims at this point, or to recommend drinking green tea, is the premise for another trial," said Dr. Hawk.
Source: http://www.medscape.com/viewarticle/773011
