Green tea is one of the most popular beverages in the world. It is believed that green tea can help prevent cancer.
A series of evidences from researches have concluded that green tea can be of use in preventing and inhibiting the growth of certain types of cancer.
Green tea contains catechins
Cancer is triggered by unnecessary growth of cells in the body. Green tea has special component called catechin which helps to kill cancer cells, without harming healthy tissues.
Green tea is made from the unfermented leaves of the Camellia sinensis plant that are rich in polyphenols such as catechins. The predominant green tea catechins are Epigallocatechin gallate (EGCG), Epigallocatechin (EGC), Epicatechin-3-gallate (ECG) and Epicatechin (EC).
The most potent catechin found in green tea, EGCG, is thought to be responsible for the many health perks that have traditionally been linked to green tea. This particular catechin has been extensively researched on for its medicinal properties including its anti-cancer potential.
How green tea help with cancer prevention?
The green tea catechins-EGCG, EGC, and EC- possess antioxidant properties, because of which they repair cell damage done by free radicals.
Free radicals are found naturally in our bodies but they are also formed with exposure to pollution and radiation. The catechins are effective in scavenging free radicals that can harm living cells.
Animal studies have shown that green tea polyphenols inhibit the spread of tumor cells and induce apoptosis, a process of cell death used by our bodies to get rid of unnecessary cells.
They also work to inhibit the formation of blood vessels induced by the tumor cells (angiogenesis) and tumor invasiveness.
Evidence that suggests green tea's anticancer effects
A large body of evidence can be found that shed a positive light on the effectiveness of green tea in prevention of certain types of cancers.
However, there isn’t any conclusive evidence that green tea can keep cancer at bay. A review of existing literature on green tea suggest that while the evidences presented are noteworthy, they do not point to convincing benefits.
Here is a list of various researches conducted over the years which establish a link between green tea and cancer prevention.
A meta-analysis of multiple studies concluded that women who drank green tea were approximately 20% less likely to develop breast cancer.
In a randomized trial, 49 men were given green tea capsules called Polyphenon E twice a day for over a year. It was observed that there was a lower rate of prostate cancer development compared to a placebo group.
A cohort study performed on 69,710 Chinese women suggested that regular green tea consumption decreased the risk of colorectal cancer.
Drinking green tea regularly may reduce the risk of ovarian cancer.
Clinical trials have suggested that green tea extract can be effective in the chemoprevention of oral cancer. 
A meta-analysis of 22 studies indicated an association between high consumption of green tea and prevention of lung cancer. It suggested that drinking two cups of green tea a day might decrease the risk of lung cancer by 18%. In contrast to this, a population based cohort study led by a Japanese team found no evidence of such association.[6, 7]
Furthermore, animal studies have shown inhibitory effects of green tea extracts and polyphenols against cell proliferation, cell invasion, and angiogenesis. These include cancer of skin, esophagus, intestine, colon, liver, pancreas, and bladder among others.
These evidences, although inconclusive, warrant a comprehensive research into the possibilities of green tea in cancer prevention.