Up to 25% of breast cancers overexpress the HER2/neu gene, which has a role in signal transduction pathways leading to cell growth and differentiation, which accounts for the relative aggressiveness of this type of breast cancer. However, there are some foods and spices that have been shown to inhibit HER2 positive (HER2+) breast cancer cell growth and proliferation.
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 webpage concerning their individual hormone receptor subtype (ER+/PR+, ER+/PR-, ER-/PR+, or ER-/PR-).

Foods that inhibit HER2+ breast cancer growth and proliferation

The following foods and spices or their components have been found specifically to inhibit the growth or proliferation of HER2/neu overexpressing breast cancer cells and have also been found to reduce breast cancer risk in general:

Foods that promote HER2+ breast cancer growth

The following foods have been shown to promote HER2+ breast cancer growth or increase HER2+ expression:
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.
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, peanuts, 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, rose or pink gold) are other potential sources of copper exposure.

Supplements for HER2+ patients and survivors

There is no supplement or combination of supplements that has been proven to reliably reduce the risk of HER2+ breast cancer recurrence in women. Attempting to increase the treatment effects of micronutrients and other dietary components by using supplements carries the risk of adverse and paradoxical effects, including promoting breast cancer growth and metastasis.
What is known is that when a beneficial micronutrient is administered at low doses by consuming food, it is likely to have subtle chemopreventive effects, whereas when the same micronutrient is administered at high doses, it is more likely to have pharmacological effects, with mostly unknown results. It is best to obtain beneficial compounds by consuming food, if possible. Supplements should be used if medically necessary or to make up for deficiencies that are difficult to correct through diet.
The following supplements generally have been found to be safe and beneficial for HER2+ patients and survivors:
CoQ10 (if needed for heart health)100 to 400 mg/day
Fish oil (from wild-caught fish)1000 to 2000 mg/day
Vitamin D1000 to 2000 IU/day
Please consult your oncology team for advice concerning your situation and dosages. It might make sense to be tested for deficiency in vitamin D and plan for follow up to determine if your reading has reached a desirable level.

Supplements that promote HER2+ breast cancer growth

The supplements below have been shown to promote HER2+ breast cancer growth or increase HER2+ expression. That is not to say that most other supplements are safe to take; there are no relevant scientific studies concerning the interactions between most supplements and HER2+ breast cancer. The supplements followed by (ER+/PR+/HER2+) have estrogenic properties that can promote the growth and proliferation of ER+ breast cancer. The remaining compounds apply to all combinations of HER2+ and hormone receptors.

Other exposures that promote HER2+ breast cancer growth

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.

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+.