A new study presented at the 2011 Era of Hope breast cancer conference has reported that resveratrol promotes mammary tumor growth and lung metastasis in a mouse model of estrogen receptor negative (ER-) breast cancer. However, a combination of grape polyphenols (resveratrol, quercetin, and catechin) was found to reduce mammary tumor growth and metastasis. Resveratrol, a phytoestrogen found in grapes and certain berries and nuts, has been found to have chemopreventive properties. Much of the work on the anti-cancer effects of resveratrol has been performed using high resveratrol concentrations in estrogen receptor positive (ER+) breast cancer cells. However, many aggressive breast cancers lose ER during the progression to metastasis.

The authors examined resveratrol's effects on breast cancer in cell and animal studies. The cell studies showed that estrogen and resveratrol have different effects on cell migration, invasion, and growth, depending on ER status. Estrogen receptors have been categorized into two types: estrogen receptor alpha and estrogen receptor beta (ERα and ERβ). Some compounds that bind to ERα do not bind to ERβ and vice versa. In ERα-/ERβ+ breast cancer cells, a low physiological concentration of resveratrol (i.e., a level that could be found in the body) reduced cell proliferation, but it also increased cell migration and invasion. The same concentration of resveratrol did not appear to influence cell growth and cell cycle progression in ERα-/ERβ- cancer cells, but it did promote cell migration.

In the first animal study, mice were used to test the influence of resveratrol supplemented diets on mammary tumor growth and lung metastasis. Resveratrol was found to increase mammary tumor growth and lung metastasis at all concentrations tested (0.5, 5, and 50 mg/kg body weight). Because resveratrol in food sources is found in combination with other polyphenols, the effects of resveratrol, quercetin, and catechin at physiological concentrations (5 mg/kg body weight) were also tested in a second animal study (more fully described elsewhere). Mammary fat pad tumors were grown from ERα-/ERβ+ and ERα-/ERβ- breast cancer cells in another group of mice. A combination of resveratrol, quercetin, and catechin was found to reduce mammary tumor growth and metastasis to bone and liver. The authors conclude that although resveratrol alone may be of limited use as a breast cancer metastasis preventive, the dietary grape polyphenols resveratrol, quercetin, and catechin in a 1:1:1 combination show promise as antimetastatic therapy.

Comments regarding the study

As the authors point out, discordance between the ER status of the primary tumor and a metastasis is not uncommon in breast cancer. Therefore even women who have been diagnosed with ER+ breast cancer may still be at risk from resveratrol supplementation, according to the study results. Although the authors in effect suggest that taking quercetin and catechin in addition to resveratrol may inhibit metastasis, this is a preliminary study. Safe and effective dosages in human beings have not been determined. Therefore, a safe and potentially effective alternative is to consume foods that contain resveratrol. Red grapes, blueberries, blackberries and cranberries are good dietary sources of resveratrol that have been found to be associated with reduced breast cancer risk.