Live from the Biggest Science Conference in the World: Cancer, Genes, and the Environment

By Karen Rowan | February 17, 2008 5:52 pm

Why do some people smoke for a short time and develop lung cancer, while others who smoke for decades live to a ripe old age, cancer-free? And why do some women with BRCA mutations develop breast cancer, while others don’t? Our genes and our environment both contribute to our cancer risks, but exactly how these interactions work is a mystery.

Cheryl Walker of the University of Texas M.D. Anderson Cancer Center says that clues to the puzzle can be found in the environment we were in before we were born. Her work shows that while developing in its mother’s uterus, a fetus may be exposed to estrogen, which can greatly impact the way the cells of the body respond when exposed to estrogen later in life.

During pregnancy, a woman’s levels of progesterone and estrogen soar, but the fetus is protected from the effects of these hormones by natural antibodies. Estrogens from the environment are just a little different from normal human estrogen, and this difference allows environmental estrogens to avoid the antibodies and affect the cells of an unborn fetus. Environmental estrogens can come from man-made sources like plastics or from natural sources like soy plants.

Walker looked at the effect of environmental estrogens on the chances of developing uterine fibroids, small tumors of the uterus that occur in 80 percent of all women. Walker exposed pregnant rats to estrogen, and she determined that there is a critical period, lasting only 3 days, during which a pregnant rat’s exposure to environmental estrogen significantly increased the chance that her unborn offspring would develop uterine fibroids.

Walker’s research suggests that exposure to estrogen during early development can prime cells to respond to estrogen exposure later in life. So two rats that have the same genes and that are exposed to the same amount of estrogen as adults can have different chances of getting uterine fibroids, depending on the estrogen they were exposed to while they were fetuses.

Still, there doesn’t appear to be a need for complete panic. During her talk, Walker sipped water out of a plastic cup.

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