Home > Kesehatan Lingkungan > AN ECOLOGICAL STUDY OF THE ASSOCIATION OF ENVIRONMENTAL CHEMICALS ON BREAST CANCER INCIDENCE

AN ECOLOGICAL STUDY OF THE ASSOCIATION OF ENVIRONMENTAL CHEMICALS ON BREAST CANCER INCIDENCE

Breast cancer is the most common malignancy in women worldwide, whereas carcinoma of the male breast accounts for <1% of all breast cancer. Besides age, geographical variation is the strongest predictor of breast cancer incidence in women and men. In general, the breast cancer incidence rates for women and men are higher in more developed countries, compared to the less developed countries. In addition, breast cancer incidence rates in US women have been rising slowly for the past two decades, which is not likely to be entirely explained by increased mammogram screening. Furthermore, studies indicate that as populations migrate from the low to high-risk geographical areas the incidence of breast cancer approaches that of the host country in one or two generations . Thus, regional differences in breast cancer incidence could provide valuable clues to the etiology of breast cancer.
The other established risk factors for breast cancer, which are primarily related to endogenous gonadal hormone influences, as well as first-degree family history of breast cancer and higher income level account for 25– 47% of breast cancer cases. It has also been estimated that another 1% of breast cancers in the U.S. may be attributable to diagnostic radiography. In women, the endogenous hormonal risk factors for breast cancer are primarily related to the reproductive cycle (i.e., early age at menarche, nulliparity, late age at first full-term pregnancy, and late age at menopause). A similar or analogous role for endogenous hormones in the etiology of breast cancer in men is suggested by observed relations with testicular dysfunction, obesity, which causes increased peripheral aromatization of estrogens, or cirrhosis, which results in a hyperestrogenic state. In addition, the histologic and clinical characteristics of breast cancer for women and men is similar, which strongly suggests that this disease in the two sexes has the same etiology . As a result of the strong association of breast cancer with endogenous estrogen excess relative to other gonadal hormone levels, it is thought that estrogen, including environmental estrogens, may play an important role in the genesis of breast cancer.
Over the last decade, several epidemiological studies were conducted to evaluate the impact of the established risk factors for breast cancer risk on the regional differences in breast cancer incidence and mortality in California with mixed results. Two of these studies indicated that the established risk factors for breast cancer did not fully explain the elevated California breast cancer rates compared to other areas of the US, whereas two other studies found that the established breast cancer risk factors accounted for the breast cancer excess in the San Francisco Bay area. The most recent of these studies, which used a prospective cohort study design and accounted for a more comprehensive subset of the established risk factors for breast cancer compared to previous studies of regional variations in breast cancer, found that these risk factors did not explain the higher breast cancer rates in the San Francisco Bay and southern coastal areas of California. This study emphasizes the importance for further investigating the importance of environmental carcinogens in the etiology of breast cancer. Environmental carcinogens may originate in the physical or chemical environment, or as part of an individual’s lifestyle. Currently, other than ionized radiation and alcohol, few environmental exposures have been clearly associated with breast cancer risk.
The public’s concern about the dangers of the chemicals used and released into the communities has increased over the last 2 decades, especially after the chemical accident that killed more than 2000 people and injured thousands of others in Bhopal, India in 1984, coupled with similar, although less devastating accidents that later occurred in the US. As a result of this concern, Congress passed the Emergency Planning and Community Right-to-Know Act (EPCRA) in 1986. As a component of EPCRA, certain manufacturers are required to report the total mass of toxic chemicals released into the environment. This information is compiled by the US Environmental Protection Agency (EPA) into a publicly accessible database known as the Toxic Release Inventory (TRI) that has been available online since 1988. TRI is considered to be the most comprehensive data source on industrial toxic emissions in the US, and as a result can be used to conduct studies that explore the link between the releases of industrial chemicals and human health. Recent research using the TRI database has been focused on developing risk assessment tools that can be used to predict health outcome results in geographical areas related to the industrial toxicants released.
In this article, we present the results of an ecological study that used the TRI database to examine the association of releases for selected industrial chemicals with invasive breast cancer incidence for women and men in Texas during years 1995 through 2000. We began the selection process for these chemicals based on a recent literature review in which they were found to be positively associated with breast cancer in epidemiological studies, and were TRI chemicals that met the Occupational Safety and Health Administration (OSHA) carcinogen standard for any neoplasm or were agents with estrogenic effects associated with breast cancer risk. OSHA uses the most current National Toxicology Program and International Agency for Cancer Research (IARC) sources to compile a list of individual chemicals that are designated as known or suspect carcinogens. The remainder of the process for selecting the industrial chemicals for the study involved excluding the chemicals that were identified in the literature review as study candidates, if they were not consistently reported to the TRI database for multiple Texas counties during the study period. The epidemiological studies related to our literature review were population-based case–control studies in women  that examined the association of occupation type with breast cancer mortality or incidence. In the study by Cantor and colleagues, it was found that workplace exposure to styrene, several organic solvents (methylene chloride, carbon tetrachloride, and formaldehyde) and several metals and metal oxides and acid mists were associated with breast cancer mortality adjusting for socioeconomic status. Of the grouped chemicals (metals, metal oxides, and acid mists) in this study, only the metals; arsenic, cadmium, chromium, cobalt, lead, and nickel, met the OSHA carcinogen standard. However, it is thought that copper may also be a breast carcinogen, since several past studies have shown that concentrations of copper along with cobalt have been shown to be significantly elevated in the serum of breast cancer patients, with higher levels observed in the advanced stages of breast cancer. Furthermore, copper as well as cobalt, nickel, chromium, and lead have been shown to bind to the estrogen receptor-a with high affinity and to stimulate the proliferation of Mcf-7 breast cancer cells. In the study by Hansen, breast cancer incidence was associated with the solvent-using industries after adjusting for socioeconomic status and reproductive factors. Likewise, in the study by Band and colleagues an excess in breast cancer cases were noted in the solvent-using occupations, such as the laundry and dry-cleaning, aircraft and motor vehicle repair, and publishing and printing industries; as well as in farm workers adjusting for age, alcohol use, family history of breast cancer, and previous breast biopsy. However, in regards to the higher risk of breast cancer in farm workers, it is important to note that there are many types of potential exposures on the farm other than pesticides, such as solvents. A large ongoing population-based study in Iowa and North Carolina that began in 1994 will help provide better answers to whether specific chemicals used in agriculture affect breast cancer risk. Furthermore, the findings in the largest study to date among women in Long Island, where there had been widespread spraying of the persistent organochlorine pesticide DDT before its ban in the US in 1972, did not support the hypothesis that organochlorine pesticides increase breast cancer risk.

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