One in eight women will develop breast cancer in her lifetime. In studies of identical twins only 27% showed the co-occurrence of breast cancer, suggesting that 73% of breast cancers can be attributed to life-style and environmental factors, rather than to genetic predisposition. Among women of the same age, the incidence of breast cancer is markedly higher for those born after 1940. The recent decline in mortality from breast cancer is due to better diagnosis and treatment.
Estrogen, the female endocrine hormone, promotes many forms of breast cancer, and hormonal therapy with estrogen is associated with an elevated risk of breast cancer. Tamoxifen, an estrogen inhibitor, is often prescribed to prevent the recurrence of breast cancer. Unlike nuclear radiation, which can directly damage or mutate DNA and lead to cancer, estrogen acts as an epigenetic factor to “turn on” uncontrolled cell division in certain women.
Synthetic chemicals to improve daily life have proliferated since World War II as we embraced “better living through chemistry.” More than 85,000 chemicals are now registered with the Environmental Protection Agency, but most of them remain untested for their effect on human health. Insecticides protect crops from insect attack and herbicides keep crops and lawns weed free. Plastics, including PVC, are ubiquitous in the environment, where they release plasticizers as they degrade.
Many pesticides have the chemical structure of the hormones that control the growth and function of the target pest. These hormones are often similar to human endocrine hormones, such as estrogen, so these chemicals are often called endocrine mimics or endocrine disruptors. Various endocrine mimics are widespread contaminants in natural waters, where they are classed as xenobiotic compounds—those whose only known origin is human activity.
I will not be the first to suggest that long-term low-level exposure to endocrine mimics could act like estrogen to promote the incidence of breast cancer in humans. The popular herbicide, glyphosate, is reported to increase the proliferation of estrogen-dependent breast cancer cells. The higher incidence of breast cancer since 1940 is consistent with the greater use and proliferation of various endocrine-like chemicals in the environment.
We may have more food, cleaner carpet, and a greater proliferation of plastic products than in earlier times, but there is a very real chance that the incidence of breast cancer in women shows that we are fouling our own nest.
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