Green Tea Extract Shows Hint of Blocking Colon Polyps in Inherited Cancer Syndrome

The trial, known as the Japan Familial Adenomatous Polyposis Prevention Study I, or J-FAPP Study I, enrolled 80 patients who were randomly split between a green tea extract group and a placebo group, with each participant scheduled to take six tablets a day for two years. The results, published in the journal Genes and Environment, describe a strong but statistically non-significant trend favoring the extract, and the authors argue that the finding justifies a larger, properly powered follow-up trial.

Familial adenomatous polyposis is an autosomal dominantly inherited disease in which affected individuals develop 100 or more neoplastic lesions, both adenomas and carcinomas, in the colorectum, leading to early-onset colorectal cancer. Because of this overwhelming polyp burden, patients with the condition form one of the highest-risk groups for colorectal cancer. Historically, the only standard method of preventing cancer in these patients was total colectomy, typically performed around the age of 20, an operation that removes the entire colon and reshapes the patient’s digestive future in a single stroke.

A newer alternative has emerged in Japan in the form of intensive downstaging polypectomy, an endoscopic procedure in which specialists aggressively remove colonic polyps, often hundreds of them, in sessions lasting around 90 minutes, with the goal of avoiding surgery altogether. The technique is now performed at many facilities across Japan. Yet it carries its own burdens: it demands advanced endoscopic skill, places a heavy workload on endoscopists, and leaves open the risk that rapidly growing polyps escape removal. For that reason, researchers have continued to seek methods that could inhibit polyp progression or reduce polyp size, complementing or reducing the need for repeated endoscopic clearing.

Chemoprevention research in familial adenomatous polyposis has tested several agents, including aspirin, nonsteroidal anti-inflammatory drugs, vitamin C, green tea extract, and dietary fiber. The NSAID sulindac showed promise in reducing colorectal adenomas in clinical trials, but serious side effects during long-term administration prevented its practical use. Selective cyclooxygenase-2 inhibitors, designed to cause less gastrointestinal mucosal damage and bleeding than traditional NSAIDs, were deemed unsuitable for chemoprevention because of cardiovascular toxicity with long-term use. Against that backdrop, green tea emerged as an attractive candidate precisely because it is a familiar dietary component with a comparatively benign safety profile.

The scientific rationale for testing green tea rests on a substantial body of observational and experimental work. Epidemiological studies have reported that green tea drinkers have a lower incidence of gastrointestinal cancers, suggesting a possible protective effect. Green tea contains large amounts of polyphenols, chiefly epigallocatechin gallate, a compound possessing antioxidant, antimutagenic, and antipromoting activities. Animal experiments reinforced the case: green tea extract prevented colorectal cancer development in rodents exposed to chemical carcinogens and suppressed intestinal tumor formation in Min mice, an animal model carrying an abnormality in the Apc gene, the same gene pathway implicated in human familial adenomatous polyposis. A small single-arm clinical trial, in which green tea extract was given to a handful of FAP patients, suggested a significant reduction in adenomas in the remaining colorectal mucosa after four years of administration.

The trial itself was a double-blind, randomized, multicenter study with enrollment running from August 28, 2000, to November 22, 2003. Participants were men and women aged 16 or older with 100 or more colorectal adenomas or a pathogenic germline variant in the APC gene, and they either had not undergone colorectal surgery or had residual colon after colectomy. Patients were randomized one to one to green tea extract or placebo using block randomization, with allocation balanced by facility and prior colorectal surgery status. The test food, supplied by Taiyo Kagaku Co., Ltd., consisted of six tablets per day taken after each meal, delivering 959.4 milligrams of green tea extract and 501 milligrams of catechins daily, an amount the authors note is equivalent to approximately ten cups of Japanese tea. The tablets were decaffeinated, containing only 0.1 milligram of caffeine each, and the placebo tablets were lactose-based and indistinguishable in appearance.

The primary endpoint was the change in colonic polyps from the lower sigmoid colon to the rectum over two years, assessed by colonoscopy with a standardized photographic protocol. Indigo carmine dye was sprayed to enhance visualization, the bowel was insufflated until cylindrical and wrinkle-free, and photographs were taken roughly one centimeter at a time as the endoscope was withdrawn. Three endoscopists who had not performed the study endoscopies and were blinded to allocation independently judged each set of images as showing increased, unchanged, or decreased polyps, with majority opinion resolving conflicts. Secondary endpoints included adverse events, colorectal cancer occurring outside the evaluation site, and tumors in other organs.

Of 92 patients invited, nine declined, and of the 83 who consented, three were excluded before randomization, leaving 40 patients in each arm. Seven patients discontinued treatment, with reasons in the green tea extract group including a rectal cancer diagnosed after bleeding in the first month, a sudden death during sleep in the 23rd month, pregnancy, and self-initiated discontinuation, and reasons in the placebo group including rectal cancer in the ninth month, pregnancy, and self-initiated discontinuation. Photographs could not be retrieved from some patients and were of insufficient quality in others, a consequence of endoscopic equipment and pretreatment methods that were not yet fully developed in the early 2000s. Ultimately, 27 patients in each group underwent evaluation at the final photograph assessment meeting, meaning roughly one-third of the randomized participants were excluded from the primary analysis.

The headline result was a risk ratio of 0.43, with a 95 percent confidence interval of 0.12 to 1.49 and a p value of 0.16, for the primary endpoint of colorectal polyp enlargement, meaning the green tea extract group tended to have fewer patients whose polyps grew, but the wide confidence interval crossing 1.0 means the difference could be due to chance. Subgroup analyses suggested the same directional tendency among men, patients aged 35 or older, and patients with a history of colorectal surgery, though none reached significance. On safety, aside from one sudden death in the green tea extract group whose causal relationship to the study the authors describe as unclear, and one colorectal cancer in each group, no serious adverse events requiring hospitalization were observed in either arm.

The authors frame the trial as the first double-blind clinical trial using green tea extract in familial adenomatous polyposis patients with colorectal polyp suppression as the endpoint, and they acknowledge candidly that the small number of evaluable cases made the result statistically insignificant despite a point estimate below 0.5. They also note that their group’s earlier double-blind randomized trial of aspirin in the same population reduced the incidence of colorectal polyps of 5 millimeters or larger, with an adjusted odds ratio of 0.37, and suggest green tea extract may have a similar effect. Listing the qualities they consider essential for a chemopreventive agent, the absence of serious side effects, low cost, and simple non-invasive administration, they argue green tea extract meets all three. The study’s limitations include the small evaluated sample, the exclusion of about a third of randomized participants with attendant risk of bias, outdated endoscopic equipment, and inconsistent patient management in an era before Japanese clinical guidelines existed. With modern intensive downstaging polypectomy now widely performed and imaging much improved, the authors conclude that green tea extract has the potential to suppress colorectal polyps in familial adenomatous polyposis and that a future large-scale trial, with sample size calculated from these results, is warranted.

Subject of Research: A randomized controlled trial of green tea extract for suppressing colorectal polyps in familial adenomatous polyposis patients

Article Title: Potential of green tea extract to suppress colorectal polyp development in patients with familial adenomatous polyposis: a double-blind, randomized controlled trial Japan Familial Adenomatous Polyposis Prevention Study (J-FAPP Study I)

Article References: Ishikawa, H., Mutoh, M., Yamane, T., Wakabayashi, K., Hirata, K., Iwama, T., Nakamura, T., Tomita, N., Matsuyama, Y., & J-FAPP Study I Group (2026). Potential of green tea extract to suppress colorectal polyp development in patients with familial adenomatous polyposis: a double-blind, randomized controlled trial Japan Familial Adenomatous Polyposis Prevention Study (J-FAPP Study I). Genes and Environment, 48(1), Article 6. https://doi.org/10.1186/s41021-026-00354-2

Image Credits: AI Generated

DOI: 10.1186/s41021-026-00354-2

Keywords: familial adenomatous polyposis, green tea extract, colorectal polyps, chemoprevention, randomized controlled trial, epigallocatechin gallate, colorectal cancer, APC gene, endoscopy, Japan, catechins, clinical trial