Green tea (Camellia sinensis) leaves contain bioactive and possibly-immunostimulatory polyphenols such as flavonoids, catechins (flavan-3 oils), and tannins, the anticancer effects of which have been assessed almost exclusively in preclinical lab experiments and epidemiological studies.1-5

Green tea and green tea extracts are widely consumed by patients with cancer. Yet overall there is no clinical evidence that green tea or its chemical components slow tumor progression in humans — and importantly, there is some evidence that green tea compounds might interfere with anticancer treatment.6

Patients whose treatment regimens include bortezomib or radiotherapy should avoid green tea, and all patients with cancer should inform their care team if they are consuming green tea or green tea supplements, as well as any other herbal supplements.

Several recent epidemiological studies do suggest possible associations between high levels of green tea consumption and a reduced risk for some cancers.7-9 The few phase 1 (safety) clinical trials of green tea and cancer that are published, however, have not yielded evidence of antitumor activity.1,10,11

Evidence in Favor

There is some evidence that topical application of green tea might speed radiotherapy skin burns.1

Phase 1 clinical trials suggest that green tea consumption is likely to be generally safe for cancer patients and people at risk of cancer. Results from the phase 1 Minnesota Green Tea Trial suggest that most adverse reactions to EGCG-rich green tea extract were mild and transient (at 843 mg daily) among postmenopausal, mostly Caucasian, women.10

The study participants experienced no serious adverse events, although green tea extract was associated with significantly higher levels of nausea and skin rash, as well as elevated alanine aminotransferase (ALT) enzyme levels compared with placebo-group study participants (6.7% vs 0.7%; P < .001).10 Green tea extract consumption was also associated with lower levels of diarrhea (P = .002).10

Systematic reviews and meta-analyses that pool data from epidemiologic and available clinical trials found possible associations between high levels of green tea (7 cups per day) or EGCG consumption and reduced risks of prostate, liver, and endometrial cancer.8,9,12,13

A recent multicenter retrospective case control study of 442 adult leukemia patients and 442 outpatient controls in China suggests that patients with leukemia were half as likely to have consumed green tea for more than 20 years as were non-leukemia patients (odds ratio [OR] 0.50; 95% CI: 0.27-0.93).15

Yet additional prospective research would be required to clarify whether this implies that green tea reduces adult leukemia risk.

There is limited preclinical evidence that green tea polyphenols (GTPs) are immunostimulatory, and that high levels of GTP intake suppresses tumor progress in lab animals (in experiments with animal models of bladder cancer, for example).4

Poor intestinal absorption and metabolic factors reduce GTC bioavailability, however, suggesting that green tea consumption alone may not capture the potential clinical benefits of GTP.16

Research and development efforts are already under way to improve GTP bioavailability for prostate cancer chemoprevention, using nanoparticle polymer formulations that “represent the main way to translate preclinical results in a real clinical scenario,” Italian researchers reported.16