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Researchers Explore Link Between Pollutants and Breast Cancer Risk (dateline December 5, 2000)

While researchers have identified several biological factors that may increase the risk of breast cancer (including age, family history, early onset of menstruation, late menopause, etc.), environmental causes for breast cancer have been more difficult to pinpoint. After a 1993 study suggested that four banned pollutants contributed to higher rates of breast cancer in certain New York counties, the Long Island Breast Cancer Study Project (LIBCSP) was developed to help identify environmental factors that contribute to breast cancer risk. A small study by the American Health Foundation is the first of more than 10 studies on this topic to be completed for the Long Island Breast Cancer Study Project.

A study conducted by the American Health Foundation and led by Dr. Steven D. Stellman and Dr. Mirjana Djordveic was released in November 2000. The study investigated DDT (dichloro diphenyl trichloroethane; an insecticide), PCB (polychlorinated biphenyl; used as coolants and lubricants in electrical equipment), and two pesticides, chlordane and hexachlorobenzene. All of these pollutants have been banned in the United States but break down very slowly in the environment.

According to the results of the study, exposure to the pollutants does not appear to be a direct cause of breast cancer. To conduct their study, Dr. Stellman and his colleagues analyzed fat tissue samples from 232 Long Island women who had been diagnosed with breast cancer and 323 Long Island women with non-cancerous breast disease or non-breast related conditions. After a quantitative analysis of the tissue, the researchers concluded that the pollutants did not exist in significantly different amounts in the two groups of women. That is, women with breast cancer did not have larger amounts of pollutant by-products per gram of tissue than women without cancer.

While the results of the American Health Foundation study contradict the previously reported link between breast cancer risk and pollutants, the researchers are quick to point out that the study is small, and therefore, the significance of the results is limited. Several other studies are expected to be published in the near future as part of the Long Island Breast Cancer Study Project and may provide a more definitive examination of the association between environmental pollutants or pesticides and breast cancer.

Many physicians and breast cancer advocates believe that environmental factors are at least partially responsible for many breast cancer cases. While the American Health Foundation did not find a link between DDT, PCB, chlordane, or hexachlorobenzene and breast cancer, Debbie Basile, president of Babylon Breast Cancer Coalition, is certain that chemicals do contribute to breast cancer. She believes that scientists need to keep investigating other chemicals or combinations of chemicals.

A high prevalence of breast cancer in certain counties spurred the Long Island Breast Cancer Study Project (LIBCSP). The LIBCSP is a multi-study project organized and funded by the National Cancer Institute, in association with the National Institute of Environmental Health Sciences (NIEHS). The project was designed to assess the relationship between pollutants and breast cancer risk in Suffolk, Nassau, and Schoharie counties in New York, and in Tolland County in Connecticut. Most of the studies for the LIBCSP are being conducted at major academic centers in the Northeastern United States, such as the State University of New York at Stony Brook and Yale University.

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. Though many of the suspected pollutants have been banned for 20 years or longer, they persist in the environment because they degrade slowly.

Researchers are also investigating several factors that may play a role in how greatly these pollutants could influence a woman’s risk of breast cancer. For example, some researchers have suggested 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.

In addition to multiple studies on pollutants and breast cancer risk, a health-related geographic information system (GIS) is being developed for the Long Island area. The system is capable of storing, manipulating, displaying, and analyzing various types of data that can be referenced by geographic location and will help researchers assess the link between environmental pollutants and breast cancer on Long Island.

Several 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.

Known risk factors for breast cancer include:

  • Age (over 50)
  • Personal or family history of breast cancer
  • Genetic (such as mutations of the BRCA1 or BRCA2 genes)
  • Previous biopsy showing non-cancerous breast conditions
  • Early onset of menstruation (before age 12)
  • Late menopause (after age 50)
  • Delayed childbirth or never having children

Researchers will continue to investigate pollutants individually or in combination to determine whether a link between these environmental factors and breast cancer incidence exists.

Additional Resources and References