The Environment & Breast Cancer


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Less than one out of every 10 cases of breast cancer occurs in women born with a genetic predisposition for breast cancer, and as many as half of all breast cancers occur in women who have no known risk factors for the disease. Patterns of breast cancer indicate the importance of environmental exposures.

We are all exposed to radiation and to hundreds, if not thousands, of chemicals every day of our lives, yet we know very little about the likely synergistic effects of these multiple exposures. An estimated 100,000 synthetic chemicals are believed to be in use today. Another 1,000 or more are added each year. More than 90 percent have never been tested for their effects on human health. Studies reveal the internal contamination of our bodies by chemicals with known carcinogenic activity.

A significant body of scientific evidence links exposure to radiation and synthetic chemicals to an increased risk of breast cancer.

Evidence That Environmental Factors Cause Breast Cancer

Ionizing radiation is the longest-established environmental cause of human breast cancer. In 2005, the National Toxicology Program classified X-radiation and gamma radiation as known human carcinogens. Radiation is a mutagen as well as a carcinogen; the same is true of some chemicals.

Compelling scientific evidence points to some of the 100,000 synthetic chemicals in use today as contributing to the development of breast cancer, either by altering hormone function or gene expression.

  • There is broad agreement that exposure over time to natural estrogens in the body increases the risk of breast cancer. Hormone replacement therapy and hormones in oral contraceptives also increase the risk. The National Toxicology Program now lists steroidal estrogen (the natural chemical form of estrogen) as known human carcinogens. The International Agency for Research on Cancer (IARC) has listed both steroidal and nonsteroidal estrogens as known human carcinogens since 1987.
  • Synthetic agents that mimic the actions of estrogens are known as xenoestrogens and are one type of endocrine-(hormone-) disrupting compound. They are present in many pesticides, fuels, plastics, detergents and prescription drugs. Chronic exposure to widespread and persistent xenoestrogens may help explain the increase in breast cancer in industrialized countries around the world. Xenoestrogens known to increase the risk of breast cancer include:
    • Bisphenol-A (BPA), one of the most pervasive chemicals in modern life, used to make polycarbonate plastic;
    • Polyvinyl chloride (PVC), used extensively in plastics including food packaging, medical products, appliances, cars, toys, credit cards and rainwear;
    • Dieldrin, a pesticide banned from all uses in 1987; and
    • Ingredients in many household products, especially cleaning agents, solvents and pesticides.
  • Elevated rates of breast cancer have been found among workers exposed to a variety of solvents in the electronics, fabricated metal, lumber, furniture, printing, chemical, textile and clothing industries.
  • Aromatic amines are a class of chemicals found in the plastic and chemical industries, in air and water pollution, diesel exhaust, tobacco smoke and in grilled meat and fish. One type of aromatic amine, o-toluidine, is known to cause mammary tumors in rodents.
  • The Environmental Protection Agency determined that 1,3-butadiene is carcinogenic to humans by inhalation and the National Toxicology Program classified 1,3-butadiene as a known human carcinogen. It is an air pollutant created by internal combustion engines and petroleum refineries. It is also used in some manufacturing processes and is found in tobacco smoke.