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A new study continues the debate on whether exposure to chemicals in the environment increases the risk of breast cancer. To date, evidence has been inconclusive, with some studies showing a link between chemicals and breast cancer and others showing no association. This latest study, based on the analysis of blood samples from cancer patients and healthy women, shows that women with breast cancer were more likely to have residue from the banned pesticides DDT and HCB in their blood. While the study does not prove that the chemicals caused breast cancer, it does raise questions about environmental risk factors for breast cancer. People are typically exposed to low concentrations of environmental chemicals through diet, water, etc. Researchers believe that certain environmental pollutants or pesticides may increase breast cancer risk because many of these compounds appear to affect the body’s metabolism of the hormone, estrogen. In fact, several experimental animal studies have shown that exposure to chemicals increases the risk of estrogen-sensitive cancers (i.e., cancers that depend on estrogen to grow). Though many of the suspected pollutants have been banned for 20 years or longer, they may persist in the environment because they degrade slowly. HCB (hexachlorobenzene) and DDT (dichlorodiphenyltrichloroethane) are both pesticides that were banned in the United States in 1965 and 1972 respectively. Given the contradictory results of several studies on DDT and HCB, Dr. C. Charlier and colleagues from the Sart Tilman University Hospital in Belgium decided to study blood samples of breast cancer patients and healthy women to determine if DDT and HCB levels differed. They analyzed blood from 159 women with breast cancer and 250 healthy women for traces of the pesticides. The results showed that levels of total DDT and HCB were significantly higher in breast cancer patients than in the healthy women. Thus, Dr. Charlier and his colleagues conclude that their "results add to the growing evidence that certain persistent pollutants may occur in higher concentrations in blood samples from breast cancer patients than [healthy women]." However, in the study, pesticide levels did not coincide with estrogen sensitive breast cancers, as previous animal studies suggested they might. Approximately 80% of breast cancers are estrogen-sensitive; that is, they depend on the hormone estrogen to grow. The remaining 20% of breast cancers do not depend on estrogen. Women with both estrogen-sensitive and non-estrogen sensitive breast cancers had pesticide residue levels in their blood in the study. While these results do seem to point to pesticides as a risk factor for breast cancer, the study does not show that the chemicals actually caused cancer. They were simply present in the blood of cancer patients of the majority of breast cancer patients but only 2.5% of the healthy women. Further research is needed to explore the relationship between pesticides and breast cancer, including a probe into how women are being exposed to these banned chemicals. Researchers are also investigating several other factors that may play a role in how greatly pollutants could influence a woman’s risk of breast cancer. For example, some research suggests that women with high body mass indexes may be at greater risk for breast cancer because the total body load of chemicals may be higher in these individuals. (Body mass index (BMI) measures a person’s total body fat and is derived by multiplying a person's weight in pounds by 703 and then dividing it twice by the height in inches. According to federal guidelines a BMI of 25 to 29.9 is considered overweight and a BMI of 30 or greater is considered obese). Also, researchers are investigating long-term risk of exposure to pollutants in utero (via the placenta) and through breast milk. The goal is to determine whether exposure to these pollutants during fetal and infant life may lead to an increased risk for cancer 20 or 30 years later in life. The prenatal period is thought to be the riskiest period in terms of exposure to harmful agents. Therefore, exposure to pollutants may be more harmful if it occurs during the prenatal period than if it occurs during adulthood. A number of small studies over the past few years have also shown a possible increased incidence of breast cancer in women who use dry cleaning services or professional lawn services. However, several experts doubt the scientific validity of these studies whose data are often contradicted in larger studies. A number of risk factors for breast cancer have already been identified. However, most of these risk factors are biological. It is estimated that 80% of women who develop breast cancer have no known risk factors for the disease, suggesting that environmental components may play a role in determining who is likely to develop the disease. Some known risk factors for breast cancer include:
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