Adequate copper is required for normal iron metabolism and blood cell formation. However, high circulating levels of copper have been linked to increased breast cancer risk. Copper concentrations tend to be elevated in breast cancer patients. Inducing copper deficiency has been shown to reduce tumor development and angiogenesis in mouse models of HER2/neu overexpressing (HER2+) and inflammatory breast cancer (IBC). A 2013 study reported that treating breast cancer patients at high risk of recurrence with tetrathiomolybdate, a copper chelator (a drug that removes copper from the body), appeared to promote tumor dormancy and help prevent relapse, especially among women with triple negative (ER-/PR-/HER2-) breast cancer. Now a report presented at the 2015 American Society for Clinical Oncology (ASCO) Annual Meeting in June has concluded that copper depletion could result in an inhospitable environment for tumor progression, especially for triple negative disease.

Copper's interaction with breast cancer

In order to grow beyond a very small size, tumors must induce angiogenesis, the growth of new blood vessels. Cancer cells induce angiogenesis during the early stages of tumor development this is a crucial step that separates preinvasive and dormant forms of cancer from invasive and metastatic growth. Copper has been shown to promote angiogenesis in existing cancers and also appears to have a role in breast cancer cell migration and invasion. Therefore, copper depletion may help prevent the spread of early-stage breast cancer. However, once breast cancer has reached stage IV, it may be too late for copper chelation to be helpful. Clinical trials have demonstrated that copper depletion is not effective in slowing the progression of advanced breast cancer.

Food and other sources of copper exposure

The following foods have high concentrations of copper:

Calf's liver or veal liver
Beef liver
Lamb liver
Calf's liver contains 12 to 15 mg of copper per 100 g, which is well above the recommended adequate intake of 0.9 - 1.3 mg per day. On the other hand, the copper content of chicken liver is only about 0.5 mg per 100g. The foods below contain far less copper than calf's liver, but are potentially significant sources of copper, depending on the frequency and volume of consumption:

Shellfish, especially oysters, squid & lobster
Sesame seeds & sesame oil
Products made from defatted soy flour, such as soy protein isolate & textured soy protein
Chocolate, cocoa powder & hot chocolate
Nuts, especially cashews, brazil nuts, hazelnuts, walnuts, pistachio nuts & pine nuts
Sunflower seeds
Soybeans
Pesto, basil
Pumpkin seeds
Sun dried tomatoes
Lentils
Multivitamins and copper jewelry (including red gold and pink gold) are other potential sources of copper exposure. It has been demonstrated that copper bracelets can deliver copper through the skin. Living near copper mining or smelting operations or working with copper can also increase copper exposure.

One study found that circulating levels of copper and the copper/zinc ratio were significantly higher in breast cancer patients compared to controls, suggesting that zinc might mitigate the cancer-promoting effects of too much copper. Women with breast cancer should not exceed the RDA (recommended dietary allowance) of approximately 0.9 mg of copper. Note that women with low iron stores are at risk of anemia if they do not have adequate copper intake.

Latest research reports copper chelation may inhibit recurrence

The report referenced at the beginning of this news story describes preliminary results of a Phase II clinical trial of copper depletion (using the copper chelator tetrathiomolybdate) in women with high-risk breast cancer who showed no evidence of disease progression at enrollment. Bone marrow-derived endothelial progenitor cells (EPCs) and copper-dependent pathways have been shown to be important in remodeling the tumor microenvironment and generating the pre-metastatic niche. The authors hypothesized that copper depletion would reduce EPCs and inhibit copper-dependent processes in breast cancer patients at high risk for breast cancer progression.

The study included 75 breast cancer patients at high risk of relapse, which was defined as having either (1) lymph node positive triple negative disease (48% of participants); or (2) stage III or IV breast cancer with no evidence of disease at enrollment. Median age was 51. Tetrathiomolybdate dosage was calibrated to maintain ceruloplasmin (a copper-carrying protein in the blood) levels of five to 17 mg/dl until the end of treatment or breast cancer recurrence. The primary study endpoint was change in EPCs during treatment with tetrathiomolybdate. Secondary endpoints included the tolerability and safety of tetrathiomolybdate, as well as its effects on other relevant markers. Treatment lasted for a maximum of 24 cycles of 28 days each. Participant have received more than 2,021 cycles to date.

After a median follow-up period of 5.6 years, the progression-free survival rate for all 75 participants from the beginning of tetrathiomolybdate treatment is 81%; the rate for all stage II or III women with triple negative disease is 94%. Treatment with tetrathiomolybdate was effective in reducing the median ceruloplasmin level from 28 at baseline to 16 after one cycle. However, copper depletion was greatest in women with triple negative disease. Tetrathiomolybdate was well tolerated; the only serious toxicities were reversible neutropenia (2.5%) and anemia (0.04%). Copper depletion was associated with a significant decrease in EPCs and another marker (LOX: lysyl oxidase) in the two-year analysis; the five-year analysis is ongoing. The authors conclude that tetrathiomolybdate is safe and well tolerated and appears to affect multiple components of the tumor microenvironment, resulting in an inhospitable environment for tumor progression. This effect is especially striking in triple negative breast cancer. Further phase III trials are warranted, according to the authors.

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.