Exposure to chemicals early in life may alter how breast tissue develops and raise the risks of breast cancer and lactation problems later in life, scientists concluded in a set of reports published Wednesday.
The scientists are urging federal officials to add new tests for industrial chemicals and pesticides to identify ones that might disrupt breast development. In some cases, they said, mammary glands are more sensitive to effects of hormone-disrupting chemicals than any other part of the body, so low levels of exposure may be causing breast changes.
"Few chemicals coming into the marketplace are evaluated for these effects," said one of the reports, based on the findings of more than 60 scientists who convened a workshop in Oakland, Calif., in 2009.
Although many experts have long debated the role of the environment in breast cancer, the possibility that chemicals are changing how and when breasts develop is a relatively new concern for scientists.
Recent animal tests show that when rodents are exposed to some hormonally active chemicals in the womb or as newborns, their mammary glands do not grow normally, and the changes can slow or speed up breast development, impair breastfeeding or cause cancerous tumors later in life. Included are estrogens used as pharmaceuticals, phytoestrogens in plants consumed as foods and synthetic compounds including bisphenol A, flame retardants and pesticides, according to the report, which was published online in the journal Environmental Health Perspectives.
Whether the same thing happens with human beings is largely unknown, although scientists say that rodent breasts develop much like human breasts, in the same stages.
"Animal studies demonstrate that early life exposure to hormonally active agents can lead to effects on mammary gland development, impaired lactation and increased susceptibility to cancer. However, the influence of environmental exposures on breast development outcomes is poorly understood, as is the relationship between breast development, lactational deficits, and breast cancer," wrote the authors, who are scientists from the National Toxicology Program, the Environmental Protection Agency and the nonprofit Silent Spring Institute.
In a companion report published Wednesday, scientists with three federal agencies who studied mice exposed in the womb to a chemical used to make Teflon found delayed breast development and impaired lactation. The effects were found in the mice at the concentrations detected in the water supply of an Ohio town near a DuPont Co. plant that uses the chemical, known as PFOA. Water supplies are not routinely monitored for it.
"If human exposures in distinct populations are approximating those provided in this study, concern over human breast health and lactational competency are justified," said the authors, led by Suzanne Fenton, a mammary gland expert at the National Toxicology Program.
Traditional animal tests required by federal officials have linked more than 200 chemicals and contaminants to breast cancer. But, in an editorial published with the three reports, Julia Brody and Ruthann Rudel of the Silent Spring Institute and Mhel Kavanaugh-Lynch of University of California said that those tests "may be missing many more" because they look only for tumors and "neglect development effects."
Breast cancer is the leading form of cancer in women, and some experts are concerned that chemicals acting like hormones may raise the risk if exposures come during critical development times. The most critical times are in the womb, and during puberty and pregnancy. During these times, hormones regulate how mammary glands grow, and if they grow abnormally, it may cause cancer and other problems later.
Developing better tests "is essential to identify chemicals that may interfere with breast development and contribute to cancer, so we can use this knowledge for primary prevention," Brody, Rudel and Kavanaugh-Lynch wrote in their commentary.
In some cases, animal studies have shown that altered breast development occurs only when a dose occurs at a certain time. For example, with atrazine, a widely used farm herbicide, delayed breast development occurred in the rodents when the pesticide dose was given 17 to 19 days after gestation, the report said. This is the time when the rodents' mammary buds are formed.
In humans, little is known about whether chemicals impair breast development or lead to breast cancer. One example, however, shows the potential risks. Pregnant women who took an anti-miscarriage drug called DES, a potent synthetic estrogen, in the 1940s through 1960s had a high rate of breast cancer, as did their daughters.
Studies also have found altered breast development in male rodents, not just females, so tests are needed on males, too, the scientists said.
The report on the workshop findings was written by Rudel and Janet Ackerman of the Massachusetts-based Silent Spring Institute, Fenton of the National Toxicology Program and Susan Euling and Susan Makris of the EPA's Office of Research and Development.
The scientists at the workshop concluded that existing animal tests are inadequate for assessing whether a chemical changes breast development.
Makris wrote in a commentary published with the report that most toxicity tests do not expose animals during sensitive stages of mammary gland development and do not adequately examine the tissues. She recommended a series of ways to expand the testing.
The National Toxicology Program, the federal agency that tests chemicals, does analyze mammary glands in some chemical assessments, but has not yet made it standard practice.
"If we care about chemicals and breast cancer, or other breast effects, we have to look at the breast tissue when we test the chemicals. That is not currently what is happening," Rudel said.
This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.