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General Information and Statistics
According to the most recent statistics provided by the National Cancer Institute, breast cancer is (aside from non-melanoma skin cancer) the number one cause of cancer-related deaths in Hispanic women. It is the second most common cause of cancer death in white, black, Asian/Pacific Islander, and American Indian/Alaska Native women.
In 2003 (the most recent numbers available), statistics revealed the following:
- 181,646 women and 1,826 men were diagnosed with breast cancer.*
- 41,619 women and 379 men died from breast cancer.*
Several risk factors have been found that may increase a woman's chances of developing breast cancer. These include the following:
- Getting older
- Early onset of menstrual period
- Starting menopause at a later age
- Being older at the birth of the first child
- Never giving birth
- Not breastfeeding
- Personal history of breast cancer or some non-cancerous breast diseases
- Family history of breast cancer (mother, sister, daughter)
- Treatment with radiation therapy to the breast/chest
- Being overweight (increases risk for breast cancer after menopause)
- Long-term use of hormone replacement therapy (estrogen and progesterone combined)
- Having changes in the breast cancer-related genes BRCA1 or BRCA2
- Using birth control pills, also called oral contraceptives
- Drinking alcohol (more than one drink a day)
- Not getting regular exercise
Metals and Cancer
Recent research indicated toxic metals, particularly cadmium, nickel, and aluminum as another cause of breast cancer. These heavy metals have been known to have specific effects on several biological systems. Dr. Maggie Louie, assistant professor in the Department of Natural Sciences and Mathematics, Dominican University of California, has received a $150,000 grant from the National Institutes of Health (NIH) in support of breast cancer research at the University. Dr. Louie's work focuses on the potential role that environmental contaminants play in the development of breast cancer.
Dr. Louie is studying how the heavy metal cadmium - an environmental contaminant that enters the body through consumption of contaminated food or water, or inhalation of cigarette smoke - contributes to the development of breast cancer. Her preliminary findings not only show that cadmium promotes breast cancer cell growth, but her lab may have also identified a potential pathway for its action.
Breast cancer results from the abnormal growth of cells in the mammary gland. The development of the mammary gland is regulated by estrogen, a hormone that binds to the estrogen receptor (ER). Most breast cancer cases initially develop as hormone-dependent cancer, in which growth and progression of the disease correlates with estrogen levels. Doctors have been battling this cancer with drugs known as anti-estrogens, which are designed to block the receptor. Although such treatments have proven successful, the cancer can later develop into a more aggressive, hormone-independent tumor.
"The mechanism of how hormone independence develops is not clear, and my current research is focused on understanding the mechanism of how hormone-refractory breast cancer develops," says Louie. "One potential mechanism may involve endocrine disruptors including heavy metals such as cadmium." Several studies conducted by researchers elsewhere back up the theory that cadmium may enhance the ER function and promote the development of breast cancer. Louie's preliminary findings show, however, that cadmium may also activate another signaling mechanism and promote breast cancer.
Stoica and others documented that cadmium mimics the effects of estradiol in estrogen-responsive breast cancer cell lines. In addition, cadmium also blocks the binding of estradiol to ER-alpha in a noncompetitive manner. This suggests that cadmium may interact with the hormone-binding domain of the receptor. Treatment with cadmium resulted in a decrease in estrogen receptor, increased growth of MCF-7 cell lines, and increased levels of progesterone receptor, pS2, and cathepsin D. "Results from this study will not only provide a better understanding of how environmental contaminants such as cadmium can promote breast cancer, but also offer new insights to how the estrogen receptor can regulate both classical and non-classical ER target gene expression," says Louie.
Research Objective
High levels of transition metals like iron, nickel, chromium, copper, and lead are closely related to free radical generation, lipid peroxidation, formation of DNA-strand breaks, and tumor growth in cellular systems. Reports in the last two decades closely relate the presence of transition metals like iron (Fe) or copper (Cu) to free radical generation via Fenton- and Haber-Weiss-reactions, ascorbate autoxidation, lipid peroxidation processes, and formation of DNA strand breaks.2,12,14,19 In turn, lipid peroxidation-induced malondialdehyde-DNA adducts can accumulate and reach high levels in the breast tissue of women with breast cancer leading to endogenous DNA modifications.24 Furthermore, ferric-ethylendiamine N,N'-diacetate (EDDA), and nitrilotriacetic acid (NTA) complexes were shown to induce free radicals and renal carcinomas in Wistar rats, demonstrating the key role of transition metals in the abnormal proliferation process.9,16 As repeated mitochondrial and nuclear DNA mutations may lead to malignant growth, we (Prof. John G. Ionescu, PhD, Jan Novotny, MD, Assoc. Prof. Vera Stejskal, PhD, Anette Loch, PhD, Eleonore Blaurock-Busch, PhD, Marita Eisenmann-Klein, MD) investigated the accumulation of 12 heavy metals in eight healthy and 20 breast cancer biopsies.
Material and Methods
Heavy metal analyses were performed on 20 frozen breast cancer biopsies and eight healthy breast tissue samples supplied by the Institute of Pathophysiology and Oncology, Charles University, Prague, Czech Republic, and the Caritas Hospital St. Josef, Regensburg, Germany.
The concentrations of iron (Fe), cadmium (Cd), lead (Pb), chromium (Cr), tin (Sn), nickel (Ni), copper (Cu), mercury (Hg), silver (Ag), gold (Au), palladium (Pd), and zinc (Zn) in the biopsy material were measured in the Spezialklinik Neukirchen, Germany, by a standardized furnace-atomic absorption spectrohotometry (AAS)-technique using a Perkin Elmer Sima 6000 AA-spectrophotometer and acidic hydrolysis as pulping procedure for sample preparation.
Additionally, heavy metal analysis in all control biopsies was done by using an inductive coupled plasma-mass spectroscopy (ICP-MS) with cell technique in the Laboratory for Micro Trace Minerals, Hersbruck, Germany. All tests were performed three times. The result per sample is the mean value of three determinations expressed in ?g/kg.
Results
The Mann-Whitney U Test was used for statistical analysis of the results. A highly significant accumulation of iron (p < 0.0001), nickel (p < 0.00005), chromium (p < 0.00005), zinc (p < 0.00001), cadmium (p < 0.005), mercury (p < 0.005), and lead (p < 0.05) was recorded in the cancer samples when compared to the control group. Copper and silver showed no significant differences to the control group, whereas tin, gold, and palladium were not detectable in any biopsies. (See Table 1.) There was no statistical difference in the heavy metal content of the control biopsies when analyzed by AAS or ICP-MS (data not shown).
Discussion
In biological systems, the concentration of redox-active transition metals capable of catalyzing and/or generating free radicals like superoxide, hydrogen peroxide, and hydroxyl radical appears to be relatively low. However, under certain pathological conditions (haemochromatosis, Wilson disease, collagenoses, and various malignancies), transition metals and their transport proteins may accumulate in different target organs inducing cellular lipid peroxidation and DNA-attack.
In this respect, the ability of excess Fe in mediating the formation of hydroxyl radicals, suppressing cellular immune functions, and promoting tumor growth is well-established. Increased Cu concentrations were also found in human lung cancer biopsies and in other tumors. Ni, Cr, and Cd have been recognized as mutagens and carcinogens through their ability to inhibit the repair of damaged DNA. In addition, they can enhance the mutagenicity and carcinogenicity of directly-acting genotoxic agents. At the same time, carcinogenic effects of Ni, directly or in association with organic compounds, have been described in the literature, and recently, higher concentrations of Fe and Ni have been found in the malignant human prostate. Inhaled particulate forms of hexavalent Cr cause lung cancer, and at the cellular level, Cr exposure may lead to cell cycle arrest, apoptosis, or neoplastic transformation.
Occupational exposure to Cd is associated with lung cancer in humans, and high Cd concentrations have been found in proliferative prostate lesions. Interestingly, Zn, as an essential element, was shown to mediate and increase tumor growth, and Zn depletion was shown to suppress tumor growth in mice and rats. Macromolecular compounds (dextrans) substituted with Hg-containing side chains were reported to promote fibrosarcoma growth in mice.
The etiology of the majority of human breast cancers is still controversial. However, hormonal influences and environmental toxic compounds inducing oxidative stress and lipid peroxidation have been suggested to play a role in breast carcinogenesis. Our data describe for the first time a major accumulation of Fe and other transition metals like Ni, Cr, Cd, Zn, Hg, and Pb in the breast cancer tissue with implications in the pathogenesis of breast cancer.
Conclusions
These data suggest that unphysiological gradual accumulation of transition metals in the breast tissue may be closely related to the malignant growth process. Evaluation of metal exposure through blood, hair, or urine provocation tests, and subsequent chelation treatment may be needed to prevent and treat metal-related breast cancer and other malignancies.
Authors
Blaurock-Busch Eleonore, PhD, Research Department, Laboratory for Micro Trace Minerals, Hersbruck, Germany
Eisenmann-Klein Marita, MD, Caritas Hospital St. Josef, Regensburg, Germany
Ionescu Prof. John G., PhD, Research Department of Spezialklinik Neukirchen, Neukirchen, Germany
L3ch Anette, PhD, Research Department of Spezialklinik Neukirchen, Neukirchen, Germany
Novotny Jan, MD, Institute of Pathophysiology and Oncology, Charles University, Prague, Czech Republic
Stejskal Assoc. Prof. Vera, PhD, Department of Clinical Chemistry, Danderyd Hospital and Karolinska Institute, Stockholm, Sweden
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