Up to 25 percent of breast cancers overexpress the HER2/neu gene. HER2/neu has a role in the signal transduction pathways leading to cell growth and differentiation, which accounts for the reputation of aggressiveness of this type of breast cancer. However, there are some foods and spices that have been shown to be especially potent in inhibiting HER2 positive (HER2+) breast cancer cell growth and proliferation and promoting apoptotic cell death. Some other foods have been found to amplify the effects of Herceptin, which is used to treat HER2+ breast cancer.
Apigenin, a flavone found in foods such as parsley, celery, guava berries, bell peppers and Chinese cabbage, has been found to increase HER2+ cell death, as well as enhancing the effectiveness of Taxol and 5-FU, which are sometimes used to treat HER2+ breast cancer. Certain anthocyanins such as cyanidin-3-glucoside have also been shown to reduce HER2+ cell proliferation, as well as potentiating the treatment effects of Herceptin.
Melatonin, which is found in almonds, cherries, tomatoes, walnuts and oats, has been shown to induce apoptosis (programmed cell death) and reduce proliferation of HER2+ breast cancer cells. Note that red meat consumption has been shown to reduce circulating melatonin.
A relatively high omega-3 to omega-6 polyunsaturated fatty acid ratio in the diet is associated with reduced risk of HER2+ breast cancer. The combination of docosahexaenoic acid (DHA, found in fatty fish) and curcumin (the main active ingredient of turmeric), has been shown to be more effective in increasing programmed cell death of HER2+ breast cancer cells than either compound used separately.
Women with HER2+ breast cancer should also review the appropriate web page concerning their individual hormone receptor subtype (ER+/PR+, ER+/PR-, ER-/PR+, or ER-/PR-).

Foods that inhibit HER2/neu breast cancer growth and proliferation

Foods and supplements that promote HER2/neu breast cancer growth

The following foods and supplements have been shown to promote HER2+ breast cancer growth or increase HER2+ expression:
Folic acid supplements
Genistein supplements (ER+/PR+/HER2+ in particular)
Ligusticum chuanxiong supplements
Milk thistle or silymarin supplements
Reishi mushroom (ER+/PR+/HER2+)
Si-Wu-Tang supplements
Soybeans (ER+/PR+/HER2+)
Soy protein isolate (ER+/PR+/HER2+)
Suan-Tsao-Ren-Tang supplements
There is some evidence that diets high in saturated fat also increase risk of HER2+ breast cancer. Although alcohol is to be avoided by all breast cancer patients and survivors, evidence to date suggests that it is particularly harmful for those with HER2+ breast cancer. Women with HER2+/ER+/PR+ disease should make a point of avoiding personal care and other products containing parabens. Exposure to bisphenol A (BPA) has been shown to increase proliferation of HER2+ breast cancer cells. In addition, cigarette smoking is associated with significantly poorer outcomes for HER2+ patients.
There have been reports that copper could promote HER2+ angiogenesis and metastasis. While copper is a vital nutrient, women with breast cancer should not exceed the RDA (recommended dietary allowance) of approximately 0.9 mg. High copper foods such as calf's liver and beef liver should be avoided. Foods with moderate copper content, such as shellfish, textured soy protein, chocolate, most tree nuts, and sunflower seeds should also be limited or avoided. Walnuts should be consumed in moderation since they contain some copper (approximately 0.45 mg per ounce). Refined walnut oil has negligible levels of copper. Multivitamins and copper jewelry (including red gold or pink gold) are other potential sources of copper exposure.

Foods that result in higher omega-3 to omega-6 polyunsaturated fatty acid ratio

The following foods are good dietary sources of omega-3 fatty acids:
Arctic char
Flaxseed oil
Lake trout
Salmon, wild
Walnuts and walnut oil

Additional comments

Breast cancer patients and survivors with HER2/neu-overexpressing breast cancer should eat a wide variety of the foods on our recommended food list and limit or avoid those on our avoid list in addition to emphasizing the foods and spices on the lists above. Please see our article on how to optimize your breast cancer diet for information on what to eat during all stages of treatment and recovery.
Below are links to recent studies on this topic. For a more complete list of studies, please click on HER2+.