Cancer becomes established away from the site of the original tumor through metastasis. In order for this to occur, one or more cells must detach from the tumor and acquire migratory and invasive capabilities. Once such cells start to divide in their new location, the new tumor must establish a blood supply through angiogenesis (the development of new blood vessels) in order to grow beyond a tiny size.
A number of foods and compounds have been shown to either to promote or reduce breast cancer metastasis in cell, animal and epidemiological studies. These studies form part of the foundation for the specific food recommendations in this website. However, there are other factors over which patients and survivors also have some control that can influence steps in the metastasis cascade and the risk of breast cancer recurrence.
The following conditions, exposures and other factors have been shown to promote breast cancer metastasis:
- Inflammation
- Excess copper intake
- Exposure to BPA, phthalates, parabens, aluminum and other carcinogens
- High omega-6 fatty acid intake
- Elevated blood sugar, including temporary elevations
- High cholesterol.
Inflammation
Breast cancer growth, invasion, and metastasis all have been shown to be promoted by systemic inflammation, a persistent state of inflammation that involves the chronic activation of the immune system. Elevated plasma C-reactive protein (CRP) levels both before and after diagnosis have been found to be associated with reduced overall and disease-free survival. CRP is a measure of inflammation that can be assessed with a routine blood test. The foods on the recommended lists for each breast cancer and treatment type amount to a very effective anti-inflammatory diet. Regular exercise also tends to reduce inflammation. For more information, see inflammation.
Excess copper intake
Copper is an essential nutrient but can fuel angiogenesis. Angiogenesis is a crucial step that separates preinvasive and dormant forms of cancer from invasive and metastatic growth. Blocking this step is an important strategy for fighting cancer. In fact, some breast cancer patients are being treated with copper chelators, which remove excess amounts of copper from the body. Unless anemic, the U.S. Recommended Dietary Allowance (RDA) for copper of approximately 0.9 mg per day for adults can be used as a guide. It makes sense not to exceed this intake, on average (but not to fall far below it either). See copper.
Exposure to BPA, phthalates, parabens, aluminum and other carcinogens
Personal care products and food packaging commonly contain BPA (bisphenol A), phthalates, parabens, aluminum and other carcinogens that have been shown to promote both breast cancer development and metastasis. Below is a list of common sources of such exposures:
- Food & soda cans, plastic bottles, plastic food packaging — BPA
- Plastic food packaging, lotions and creams — phthalates
- Cosmetics, personal care products, processed food — parabens
- Face creams, hair oil, hair root stimulator — estrogens
- Personal care & pharmaceutical, household products — triclosan, an antimicrobial endocrine disruptor
- Hair dyes, occupational exposure to dyes & pigments — endocrine disruptors
- Antiperspirants, aluminum cookware — aluminum
- Household insecticides — lambda-cyhalothrin
- Synthetic fireplace logs — polycyclic aromatic hydrocarbons (PAHs)
- Air pollution — PAHs and other carcinogens
- Cigarette smoke — PAHs, cadmium & other carcinogens.
High omega-6 fatty acid intake
All vegetable and seed oils contain a variety of fatty acids, however omega-6 fatty acids predominate. A low dietary omega-3 to omega-6 fatty acid ratio is associated with increased risk of breast cancer and its recurrence. In addition, linoleic acid, an omega-6 fatty acid found in abundance in vegetable oils such as corn oil, safflower oil, soybean oil, and sunflower oil, is suspected of promoting breast cancer directly. Fatty fish, flaxseed oil and walnut oil are good sources of omega-3 fats. Note that olive oil, the most abundant source of oleic acid, an omega-9 fatty acid, has also been found to have strong chemopreventive activity. This beneficial property appears to be more the result of the oil’s polyphenol rather than its oleic acid content (studies using pure oleic acid have had mixed results). For more information, see olive oil, fatty fish, soybean oil.
Elevated blood sugar
High blood sugar and insulin resistance are also risk factors for breast cancer and metastasis. Diets with a glycemic load (heavy in foods that cause a rapid jump in blood sugar, such as processed foods made with refined starches, potatoes and sweets) appear to increase the risk of breast cancer even in women who are not overweight through higher levels of blood glucose and insulin levels, sex hormones, and insulin-like growth factor 1 (IGF-1). IGF-1 promotes breast cancer by inhibiting cellular processes designed to repress breast cancer growth. This means avoiding a high glycemic load diet. However, it also means avoiding individual meals or snacks that cause spikes in circulating blood sugar and insulin. See glycemic load, insulin resistance, metabolic syndrome, type 2 diabetes.
High cholesterol
High levels of LDL cholesterol (the "bad" cholesterol) and high triglycerides have both been shown to promote breast cancer metastasis. Increases in circulating cholesterol have been shown to accelerate the development of mammary tumors and increase tumor aggressiveness in mouse models of breast cancer. For example, in one study, mice fed a high cholesterol diet (designed to approximate levels in a typical unhealthy diet) developed larger tumors that were faster growing and metastasized more easily compared to mice on a control diet. In addition, high saturated fat consumption is associated with reduced breast cancer survival.
However, note that breast cells have the propensity to accumulate cholesterol. Circulating cholesterol levels have been observed to be reduced during mammary tumor development in mice, providing evidence of increased use of cholesterol by such tumors. In fact, low cholesterol is also associated with heightened breast cancer risk in women, possibly because undiagnosed tumors are already using cholesterol. Some researchers have theorized that breast cancer cells might migrate to seek out cholesterol by invasion when their needs are not being met in their local environment, suggesting that sharply lowering cholesterol levels could backfire. See cholesterol.
We have provided links to relevant articles or tags above and a limited number of studies below. However, a search in the ffbc search box near the top of this page (under the photo) could also be useful.