Chemical & Engineering News  [Printer-friendly version]
December 6, 2006


[Rachel's introduction: A common chemical in plastics has now been
linked to breast cancer. If this hypothesis is correct, breast cancer
is triggered by exposure that occurs in the womb.]

By Bette Hileman

A new study finds the strongest evidence yet for the hypothesis that
widespread environmental exposure to bisphenol A during fetal life
causes breast cancer in adult women. The research, led by Ana M.
Soto, professor of anatomy and cellular biology at Tufts University
School of Medicine, in Boston, was published Dec. 6 in the online
edition of Reproductive Toxicology (DOI: 10.1016/j.reprotox.2006.10.0

Soto and her colleagues exposed pregnant rats to bisphenol A at doses
ranging from 2.5 to 1,000 micrograms per kg of body weight per day. By
the time the pups exposed at the lowest dose reached the equivalent of
puberty (50 days old), about 25% of their mammary ducts had
precancerous lesions, a proportion three to four times higher than
among the nonexposed controls. Mammary ducts from all other exposure
groups showed elevated levels of lesions. Cancerous lesions were found
in the mammary glands of one-third of the rats exposed to 250

Bisphenol A, a known estrogenic compound, is ubiquitous in the
environment. Many people receive exposures of about 2.5
micrograms/kg/day, and mammary gland development in rats and humans is
very similar. Therefore, Soto says, "bisphenol A could be one factor
causing the increase in breast cancer incidence over the past 50

Bisphenol A is used in the manufacture of polycarbonate plastics and
epoxy resins. It is found in many food and beverage containers,
including baby bottles. It is also found in canned food linings and
dental composites, and it leaches from all of these products. In one
study, Soto notes, urine samples from 95% of the human subjects
contained the chemical.

According to Soto, a large body of previous research suggests
bisphenol A might cause breast cancer. One study shows that the
daughters of women who took the potent synthetic nonsteroidal estrogen
diethylstilbestrol (DES) during their pregnancies between 1948 and
1971 have 2.5 times the normal incidence of breast cancer. Bisphenol
A, which is structurally similar to DES, may act by a similar
mechanism, she explains.

"What is important to note is that Soto's research is not a one-shot
finding," says Frederick vom Saal, professor of biology at the
University of Missouri. "It follows five years of research
demonstrating precancerous changes in the mammary glands of mice with
prenatal bisphenol A exposure. Now, Soto has switched to the rat,
which is considered a much better animal model for studying human

The Environmental Protection Agency has set a safe human intake dose
of 50 micrograms/kg/day for bisphenol A. "On the basis of the effects
observed in recent studies, this seems to be an unsafe level," Soto

Copyright 2006 American Chemical Society