A new study suggests that early exposure to a chemical found in hard, clear plastics and the linings of cans may cause changes in breast tissue, predisposing laboratory animals to breast cancer.
The study, released yesterday in the journal Molecular Endocrinology, adds to a growing body of evidence showing that small amounts of the chemical bisphenol A, or BPA, can cause irreparable damage to developing animals.
"I want it to be clear that we do not provide evidence that BPA exposure causes breast cancer per se," said Cathrin Brisken of the Swiss Institute for Experimental Cancer Research, co-author of the study. "We do provide evidence that BPA exposure alters mammary gland development and that this may increase the predisposition of the breast to breast cancer."
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However, Steve Hentges, spokesman for the American Chemistry Council, a plastics industry lobbying group, was not so sure.
He said there were experimental limitations, including differences in the ways different litters responded, and he underscored the authors’ assertions that the study does not show a direct link between the chemical and breast cancer.
“Regardless of the experimental limitations, the relevance of the findings to breast cancer in humans is uncertain,” he said.
The study examined female offspring of mice exposed to environmentally relevant amounts of BPA while pregnant and nursing. The mother mice were dosed with the chemical through drinking water.
The researchers found that the mammary glands of young mice exposed to the chemical in the womb and through breast milk showed an increased sensitivity to the hormone progesterone. Progesterone exposure has been linked to breast cancer in humans.
These young mice also had a large increase in the numbers of cells in their milk ducts when compared with mice whose mothers had not been fed BPA. This increase mirrors the reaction of both humans and mice that were exposed to diethylstilbestrol, or DES, in the womb.
DES was used between the 1940s and early 1970s to prevent miscarriage and pregnancy complications, but was pulled from the market when daughters of these women began showing high rates of a rare vaginal cancer. Daughters of DES women also have a nearly twofold likelihood of getting breast cancer in their 50s, compared with women whose mothers did not take the drug.
“While we cannot extrapolate these results directly from mice to humans, the possibility that some of the increase in breast cancer incidence observed over the past decades may be attributed to exposure to BPA cannot be dismissed,” Brisken said. “Our study suggests that pregnant and breastfeeding mothers should avoid exposure to BPA, as it may affect their daughters’ breast tissue.”
“This is really an important piece of research,” said Jeanne Rizzo, president and CEO of the Breast Cancer Fund, a San Francisco-based nonprofit that advocates for the elimination of breast cancer. “It validates other work that has been done and brings the focus to the pregnant mother, the in utero exposure that’s so critical to our understanding of the influence on breast development.”
She said that based on this research, she would advise all pregnant women to do all they can to avoid BPA exposure.
“Don’t eat canned foods, buy glass, avoid plastic,” she said. “You can do a lot to cut back on your exposure.”
The research was supported by the Swiss government.