Green Tea (Camellia sinensis) leaves, which have not gone through an oxidation process, have the richest nutrient profile among all varieties of tea. Research shows that people who drink four or more cups of green tea each day have a lower overall risk of cancer and women who frequently drink green tea have a lower overall risk (or "lower overall incidence") for breast cancer.

Green tea contains phytonutrients called polyphenols, and in particular EGCG or epigallocatechin-3-gallate, which is a compound that protects against cancer. Lab tests and animal studies have shown  that EGCG works by inhibiting an enzyme that catalyzes cancer cell growth. EGCG also helps prevent cancer development by acting as a powerful antioxidant, which neutralizes chemicals known as free radicals.  Free radicals damage cells, which overtime, can lead to cancer.

It is best to use pure organic loose leaf tea, because processing degrades the nutrient content.  Before taking an EGCG supplement, consult with Dr. Phelts, in Manhattan, New York, to ensure the product is pure and contains the appropriate potency for your health concerns.  Also, green tea is not appropriate for everyone. For example, individuals suffering from adrenal conditions should not take green tea, because of its caffeine content.

References
MSKCC.org "Green Tea" (Sloan Kettering Cancer Center) Information for Patients & Healthcare Providers. Accessd 4 Aug 2019 https://www.mskcc.org/cancer-care/integrative-medicine/herbs/green-tea

Ganmaa D., Willett, W.C., Li, T.Y., et al., "Coffee, Tea, Caffeine and Risk of breast Cancer: A 22-year follow-up." International Journal of Cancer (2008),122(9): pp.2071–2076 http://www.ncbi.nlm.nih.gov/pubmed/18183588

Manach, C., Scalbert, A. et al., "Polyphenols: Food Sources and Bioavailablity." Am J Clin Nutr (May 2004), 79:5, pp 727-747. Accessed on 3 Aug 2019: http://ajcn.nutrition.org/content/79/5/727.full

Purdue News online. "Study Finds How Green Tea May Reduce Cancer." Accessed on 3 Aug 2019: http://www.purdue.edu/uns/html4ever/1999/9901.Morre.greentea.html
NIH: National Cancer Institute.gov "Tea and Cancer Prevention." Accessed on 2 Aug 2019: