Research suggests that tea may help protect against cancer.   Below are some examples:

Bladder cancer.  One study compared people with and without bladder cancer.  Researchers found that women who drank black tea and powdered green tea were less likely to develop bladder cancer. Another clinical study by the same group of researchers revealed that bladder cancer patients (particularly men) who drank green tea had a substantially better 5-year survival rate than those who did not. 

Breast cancer. Laboratory research suggests that polyphenols in green tea inhibit the growth of breast cancer cells. In a clinical study of 472 women with various stages of breast cancer, researchers found that women who consumed the most green tea experienced the least spread of cancer (particularly premenopausal women in the early stages of breast cancer). They also found that women with early stages of the disease who drank at least 5 cups of tea every day before being diagnosed with cancer were less likely to suffer recurrences of the disease after completion of treatment. However, women with late stages of breast cancer experienced little or no improvement from drinking green tea. In terms of breast cancer prevention, the studies are inconclusive.

Colorectal cancer. Results on the effects of green tea on colon or rectal cancer are conflicting. Some research shows decreased risk in those who drink the tea, while others show increased risk. Further research is needed.

Esophageal cancer. Some laboratory research has found that green tea polyphenols inhibit the growth of esophageal cancer cells. However, clinical studies have produced conflicting findings. For example, one large-scale population-based clinical study found that green tea offered significant protection against the development of esophageal cancer (particularly among women). Another population-based clinical study revealed just the opposite. In fact, the stronger and hotter the tea, the greater the risk. Given these conflicting results, further research is needed.

Lung cancer. Green tea polyphenols have been shown to inhibit the growth of human lung cancer cells.  However, few clinical studies have investigated the link and even these studies have been conflicting. One population-based clinical study found that Okinawan tea (similar to green tea but partially fermented) was associated with decreased lung cancer risk, particularly among women. A second clinical study revealed that both green and black tea significantly increased the risk of lung cancer. As with colon and esophageal cancers, further clinical studies are needed before researchers can draw any conclusions.

Ovarian cancer. Clinical research conducted on ovarian cancer patients in China, researchers found that women who drank at least one cup of green tea per day survived longer than those who didn’t drink green tea. In fact, those who drank the most green tea, lived the longest.

Pancreatic cancer. In one large-scale clinical study, researchers compared green tea drinkers with non-tea-drinkers, and found that those who drank the most tea were significantly less likely to develop pancreatic cancer. This was particularly true for women. Men who drank the most tea were 37% less likely to develop pancreatic cancer. However, it is not clear from this research whether green tea is solely responsible. 

Prostate cancer. Research has found that green tea extracts prevent the growth of prostate cancer cells. In a large clinical study conducted in Southeast China, researchers found that the risk of prostate cancer declined with increasing frequency, duration and quantity of green tea consumption. However, both green and black tea extracts also stimulated genes that cause cells to be less sensitive to chemotherapy drugs. Given this potential interaction, sometimes physicians recommend that people should not drink black and green tea (as well as extracts of these teas) while receiving chemotherapy. 

Skin cancer. The main polyphenol in green tea is epigallocatechin gallate (EGCG). Research suggests that EGCG and green tea polyphenols have anti-inflammatory and anti-cancer properties that may help prevent the onset and growth of skin tumors. 

Stomach cancer. Laboratory studies have found that green tea polyphenols inhibit the growth of stomach cancer cells, but clinical studies have been less conclusive.  Further clinical studies are underway to determine whether green tea helps reduce the risk of stomach cancer.