Breast Cancer: It's Not All In The Genes

October is Breast Cancer Awareness Month, and before it ends an additional 14,800 women in the U.S. will be diagnosed with the disease. Roughly one of every nine women will develop breast cancer in her lifetime. While genes play a role in many cases of breast cancer, roughly 70 percent of diagnosed women have non-inherited cancer. For these, we have to look at what we do and the world around us.

Some environmental causes are established. Having children late in life and early onset of puberty both increase breast cancer risk. Exposure to radiation from chest x-rays during childhood and taking hormone replacement therapy are also known to increase risk. Breast cancer rates are higher in women who are obese, women who gain weight during adulthood and those who drink alcohol routinely. On the bright side, vigorous exercise for 45 to 60 minutes five or more days per week can lower breast cancer risk in all women, studies have shown. And for postmenopausal women, any regular exercise performed can help.

Recent research into other factors, however, has returned intriguing results on contaminants ranging from pesticides to tobacco smoke. Here's a roundup:

Chemicals in the Environment

Increasingly, studies are finding that chemicals common in the world around us play a role in the development of breast cancer. These chemicals may contribute to breast cancer risk by damaging DNA, promoting tumor growth, or altering mammary gland development both before birth, during puberty, and during and after pregnancy.

In a review of the studies by the Silent Spring Institute, researchers identified 216 chemicals that were linked to breast cancer in at least one animal study. These included pesticides, dyes, pharmaceuticals and hormones as published in the journal Cancer in May 2007. Twenty-nine of these chemicals are produced in the U.S. at greater than one million pounds per year, 35 are air pollutants and 73 have been found in consumer products or as food contaminants.

Dioxins

Dioxins in the fat of milk, meat and fish are among those chemicals most strongly linked to breast cancer. Known to affect mammary gland architecture in animal studies, dioxin can have long-lasting effects on breast development if exposure occurs in utero, during a time corresponding to the first trimester of pregnancy, when some women may not even know they are pregnant. If animals with altered mammary gland development due to in utero dioxin exposure go on to mate and rear offspring, the mammary glands of their offspring are also altered, indicating that exposure to this environmental toxicant can alter breast development in multiple generations, according to the June 2006 issue of Endocrinology. Dioxin can also harm breast development if exposure happens during the other two critical periods, puberty and during lactation.