SAN FRANCISCO-Retrospective and laboratory studies have suggested that green tea might be useful for both the prevention and treatment of cancer. Two presentations at the 93rd Annual Meeting of the American Association for Cancer Research, however, showed conflicting results on the effectiveness of this beverage as an anticarcinogenic agent.
SAN FRANCISCORetrospective and laboratory studies have suggested that green tea might be useful for both the prevention and treatment of cancer. Two presentations at the 93rd Annual Meeting of the American Association for Cancer Research, however, showed conflicting results on the effectiveness of this beverage as an anticarcinogenic agent.
While one study showed that drinking green tea is linked to a dramatically reduced risk of developing certain gastrointestinal (GI) cancers, another study found that drinking green tea did not have a therapeutic effect in men with advanced prostate cancer.
In the epidemiological study, which used data from the Shanghai Cohort, researchers found that men who frequently drank green tea were much less likely to develop gastric and esophageal cancer, compared with men who drank this beverage infrequently (abstract 2354).
The Shanghai Cohort consists of 18,244 men between the ages of 45 and 64 who had no history of having cancer at study entry and who live in Shanghai, China. Each subject was interviewed and provided a blood and urine sample at study entry. The group has been followed for up to 12 years.
The Shanghai study compared baseline levels of two polyphenols found in green tea, epigallocatechin (EGC) and epicatechin (EC), and their metabolites in urine samples provided by 190 subjects who later developed gastric cancer, 42 who eventually developed esophageal cancer, and 772 controls who were matched for age, date of sample collection, and neighborhood of residence.
"After excluding subjects with less than 4 years of follow-up, the presence of EGC in the urine was related to an about 50% reduction in the risk of developing gastric and esophageal cancer," said Can-Lan Sun, MD, a researcher in the Department of Preventive Medicine, USC/Norris Comprehensive Cancer Center, Los Angeles. No such association was noted for EC.
Dr. Sun noted that EGC is a more specific marker for green tea, while EC is found in other commonly ingested foods and beverages such as apples, wine, and chocolate.
The risk reduction was primarily seen in men who had low levels of serum carotenes, which, like EGC and EC, are antioxidants. "It appears that tea poly-phenols may play an important protective role in people who have low levels of other antioxidants," Dr. Sun said.
Results of a study from the North Central Cancer Treatment Group (NCCTG) indicate that green tea polyphenols do not play a therapeutic role in advanced prostate cancer (abstract 2444).
Forty-two men with metastatic androgen-independent prostate cancer were followed at 22 NCCTG institutions. Individuals on LHRH agonists were allowed into the study, but men were not eligible if they had been treated with other cancer therapies during the previous 4 weeks or with a long-acting antiandrogen agent within the previous 6 weeks.
Each subject agreed to ingest a total of 6 g of green tea concentrate daily, the equivalent of approximately 12 cups of green tea each day. Each gram provided 100 calories as well as some caffeine.
Although laboratory studies have shown that prostate cancer cells die when exposed to green tea polyphenols, the clinical results were unimpressive. Tumor response was defined as a 50% decline from baseline PSA. Only one patient experienced such a decrease in PSA level, and after this transient decline, his PSA value began to increase.
The investigators had initially planned to follow the subjects every month for at least 4 months. While many of the men did continue in the study for the full 4 months, some individuals dropped out much earlier because of the side effects they experienced during the study.
"We found that approximately 70% of patients had some degree of toxicity. It was usually very mild," reported Aminah Jatoi, MD, assistant professor of oncology, Mayo Clinic, Rochester, Minnesota. However, there were six instances of grade 3 events and one grade 4 event.
Dr. Jatoi hypothesized that the high caffeine intake was responsible for most of the side effects that were associated with green tea use in this study. The researchers did not provide decaffeinated tea due to concerns that decaffeination might also remove compounds with antineoplastic properties.
Dr. Jatoi did not rule out the possibility that there might be a role for green tea in other clinical settings, such as cancer prevention or, perhaps, treatment of earlier prostate cancer. "But, at least at this point, we’re not planning such studies," she said.