From Slate:

The last quarter of a century has taught science some newfangled things about breasts. For one thing, they appear to be showing up earlier in young girls, with possible consequences for breast cancer later on. For another, the way they grow and develop varies from woman to woman, and—if lab animals are any indication—normal exposures to commercial chemicals can alter that process. The growing human breast is also more vulnerable than we thought. Data from atomic-bomb survivors in Japan show that it was adolescents—not grown women—near the explosions who were most likely to develop breast cancer in later years. Since then, there’s been similar data for girls who were exposed to medical X-rays or radiation therapy, as well as research showing that the pesticide DDT, now banned but pervasive in the 1950s and 1960s, is associated with a higher risk of breast cancer in women exposed as girls.

So it may come as a surprise that the federal agencies responsible for public health don’t routinely take childhood exposures into account when testing whether commercial chemicals cause mammary tumors. In fact, in many lab-animal tests, they don’t bother to look at the mammary gland at all. Breast cancer may be the No. 1 killer of middle-aged women in the United States, but as a new set of reports makes clear, the breast is a major blind spot in federal chemical-safety policy. “They just throw the mammary glands in the trash can,” says Ruthann Rudel, research director with the nonprofit Silent Spring Institute and lead author of one of the papers, a review of the latest science on mammary gland development and toxic exposures.

The reports, published last week in the journal Environmental Health Perspectives, grew out of a 2009 workshop on mammary gland risk assessment, which involved scientists from federal and international agencies as well as independent groups. Breast cancer is just one of the areas federal agencies neglect, the reports show, along with health issues surrounding lactation and the timing of breast development in puberty. “Few chemicals coming into the marketplace are evaluated for these effects,” state Rudel and her co-authors.

But blowing off these tests is a big mistake. The mammary gland—the breast’s intricate milk-making structure—is uniquely sensitive to toxic chemicals, says Suzanne Fenton, a reproductive endocrinologist with the National Toxicology Program of the National Institutes of Health, and a co-author of the science review. In both rodents and humans, it starts to develop in the fetus, undergoes a colossal growth spurt at puberty, and doesn’t fully develop until late pregnancy. During these times, its cells appear particularly vulnerable to carcinogens and other organ-altering substances. While lab rats and mice aren’t perfect proxies for humans, their mammary glands undergo similar development patterns under similar hormonal influences, says Fenton.

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