The Environment and Breast Cancer

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Written by the Dr. Susan Love Research Foundation

We launched the Army of Women^® and the Health of Women [HOW] Study because we wanted to advance research into the cause—and prevention—of breast cancer.

It is widely accepted that breast cancer is caused by a combination of genetic, hormonal and environmental risk factors.

Your genes, you are born with. Your estrogen (hormonal) risk factors are linked to the age at which you begin menstruating and go into menopause; whether you use birth control pills or hormone replacement therapy, and for how long; and if you had children, at what age, and how long you may have breastfed them.

Environmental factors don’t just mean chemicals in the environment. The “environment” also includes behavioral factors like exercise, diet and alcohol consumption, and physical factors like radiation. It can also include social, economic, and cultural factors that influence your diet or might determine what chemicals you are exposed to.

But teasing out these environmental factors as well as looking at how they might interact is far from easy. Studies have found that breast cancer risk increases in women who move from low-income countries to high-incomes countries, which points to environmental risk factors. All too often, though, people see these findings and immediately point the blame at the chemicals used in the US while downplaying our American lifestyle, which is known for its abundance of fast-food restaurants, super-sized servings, and culture of driving—which are linked to obesity and, in turn, increased breast cancer risk.

Even if a study finds a correlation between, say, blood levels of a certain chemical and breast cancer, it doesn’t mean that the substance caused the breast cancer. Our bodies are far more complicated than that. Also, research suggests that when you are exposed to a carcinogen matters, too. Scientists refer to time periods in a woman’s life, such as puberty, when these exposures might matter most as “windows of susceptibility,” and they are trying to learn more about them.

Exposure to the drug diethylstilbestrol (DES) is a good example of how timing might matter. DES is a synthetic form of estrogen that was used between the 1930s and the 1960s to reduce the risk of miscarriage. Today, we know that daughters born to women who were taking that drug have an increased risk of developing breast cancer and clear cell adenocarcinoma, a cancer of the vagina and cervix. This would suggest we all stay clear of DES—which is why people are often surprised to learn that in postmenopausal women, DES can be an effective breast cancer treatment.

Endocrine disruptors, chemicals that may increase breast cancer risk because they change the amount of estrogen in the body, are another example. It’s easy to find people who point to endocrine disruptors as the cause of breast cancer. But not all endocrine disruptors are inherently bad. Tamoxifen—which disrupts estrogen’s path to the breast—and the aromatase inhibitors—which block an enzyme called aromatase that turns androgens into estrogen—are effective breast cancer treatments precisely because they disrupt estrogen production.

In its report “Reducing Environmental Cancer Risk,” the President’s Cancer Panel emphasized not only the need for more research on environmental risk factors but also how complex this type of research can be.

As you know, Dr. Susan Love Research Foundation would never shy away from something complex. That’s why our Army of Women will soon be recruiting women in the San Francisco Bay Area for a study investigating how chemicals in the environment might affect breast cancer cells and our Health of Women [HOW] Study now contains a questionnaire to learn more about environmental exposures over time.

We would be naïve to think that either of these studies will give us “the” answer. But  they will give us information that we can use to learn more about environmental and hormonal factors that interact with our genes and may set the stage for breast cancer to occur.

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