While population studies have produced inconsistent results as to whether green tea consumption reduces the risk of breast cancer, green tea is associated with reduced risk of breast cancer recurrence. This appears to be at least in part because the green tea polyphenol epigallocatechin gallate (EGCG) increases the effectiveness of some forms of breast cancer treatment.
Now a new study has reported that EGCG can slow the development of tamoxifen resistance in hormone receptor positive breast cancer cells.
Green tea increases effectiveness of some breast cancer treatments
EGCG has been shown to potentiate the efficacy of radiation treatment in breast cancer patients by increasing radiation-induced apoptosis (programmed cell death). EGCG increases the treatment effects of Herceptin in HER2 overexpressing (HER2+) breast cancer cells. EGCG has also been shown to enhance the cytotoxicity of Taxol. On the other hand, green tea should not be consumed during Adriamycin chemotherapy because of its caffeine content (caffeine protects cancer cell DNA from the cytotoxic effects of Adriamycin).
Latest research demonstrates that EGCG reduces tamoxifen resistance
The study referenced at the beginning of this news story was designed to investigate whether EGCG can influence the development of tamoxifen resistance in hormone receptor positive (ER+/PR+) breast cancer cells. Although ER+ breast cancer survival has increased as a result of anti-estrogens such as tamoxifen, many women develop resistance to the treatment.
To conduct the study, the authors first developed a cell culture model of tamoxifen resistance using ER+/PR+ MCF-7 breast cancer cells. This was accomplished by using a prolonged culture of MCF-7 cells exposed to increasing concentrations of tamoxifen. The treatment served to apply selection pressure for the cells to acquire resistance to tamoxifen. The surviving cells were found to maintain their tamoxifen resistance even after removal of the tamoxifen treatment.
The authors then tested the influence of EGCG using this long-term cell culture model by culturing groups of MCF-7 cells with various levels of tamoxifen and EGCG. The breast cancer cell growth rate was recorded for each treatment iteration. Initially, the cells grew at the same rate regardless of whether they were exposed to tamoxifen alone or tamoxifen plus EGCG. However, eventually the growth rate of EGCG-treated breast cancer cells was delayed compared to cells treated with tamoxifen only. In addition, the cells that had undergone multiple generations of treatment with EGCG were shown to retain their sensitivity to tamoxifen.
The authors conclude that EGCG might delay the development of tamoxifen resistance in breast cancer cells.
Please see our articles on green tea and what to eat during tamoxifen treatment for more information.
Selected breast cancer studies
Intracellular Signaling Network as a Prime Chemotherapy Target of Green Tea Catechin, (–)-Epigallocatechin-3-gallate
Singh BN, Shankar S, Srivastava RK. Intracellular Signaling Network as a Prime Chemotherapy Target of Green Tea Catechin, (–)-Epigallocatechin-3-gallate. Nutrition, Diet and Cancer. Springer Netherlands; 2012;:339-376 10.1007/978-94-007-2923-0_15
Anti-Cancer Activities of Tea Epigallocatechin-3-Gallate in Breast Cancer Patients under Radiotherapy
Zhang G, Wang Y, Zhang Y, Wan X, Li J, Liu K, et al. Anti-Cancer Activities of Tea Epigallocatechin-3-Gallate in Breast Cancer Patients under Radiotherapy. Current Molecular Medicine. Bentham Science Publishers Ltd.; 2012; 12:163-176 10.2174/156652412798889063
Green tea consumption and breast cancer risk or recurrence: a meta-analysis
Ogunleye AA, Xue F, Michels KB. Green tea consumption and breast cancer risk or recurrence: a meta-analysis. Breast Cancer Research and Treatment. Springer Science and Business Media LLC; 2009; 119:477-484 10.1007/s10549-009-0415-0
(-)-Epigallocatechin-3-gallate downregulates Pg-P and BCRP in a tamoxifen resistant MCF-7 cell line
Farabegoli F, Papi A, Bartolini G, Ostan R, Orlandi M. (-)-Epigallocatechin-3-gallate downregulates Pg-P and BCRP in a tamoxifen resistant MCF-7 cell line. Phytomedicine. Elsevier BV; 2010; 17:356-362 10.1016/j.phymed.2010.01.001
(-)-Epigallocatechin gallate sensitizes breast cancer cells to paclitaxel in a murine model of breast carcinoma
Luo T, Wang J, Yin Y, Hua H, Jing J, Sun X, et al. (-)-Epigallocatechin gallate sensitizes breast cancer cells to paclitaxel in a murine model of breast carcinoma. Breast Cancer Research. Springer Science and Business Media LLC; 2010; 12 10.1186/bcr2473
EGCG Stabilizes p27kip1 in E2-Stimulated MCF-7 Cells through Down-Regulation of the Skp2 Protein
Huang H, Way T, Lin C, Lin J. EGCG Stabilizes p27kip1 in E2-Stimulated MCF-7 Cells through Down-Regulation of the Skp2 Protein. Endocrinology. The Endocrine Society; 2008; 149:5972-5983 10.1210/en.2008-0408