What Causes Breast Cancer? These Families Want To Help Find Out

At 48, Jenny Singleton got breast cancer. At 66, her mother did, too.

"When my breast cancer was diagnosed, I immediately thought we must have a gene for it," Jenny Singleton said. "So I was tested and I didn't have the BRCA gene. And so that's often left me wondering, well, then why is it that my mom and I both got breast cancer?"

Cancer susceptibility genes are estimated to account for only 5 to 10 percent of breast cancers overall. Now the Singletons and thousands of other families are part of a study that is looking to see if there is evidence that environmental exposures in the uterus during pregnancy could account for some breast cancers later in life.

From 1959 to 1967, the group's researchers enrolled some 20,000 pregnant women — including Jenny's mother, Bernice — in a long-term study to track their health and the health of their children.

Over the past five decades, the researchers have tracked those families, using the data to investigate everything from the effects of smoking and exposure to pesticides during pregnancy, to possible causes of schizophrenia.

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Cohn is using blood samples taken during pregnancy to test her hypothesis that pregnancy is a particularly vulnerable time to be exposed to environmental chemicals. "To our knowledge, we're doing the very first what I call 'womb to breast cancer' study in the world," she said.

Health researchers in this field sometimes say that genetics load the gun, but the environment pulls the trigger. But finding that trigger is hard. Cohn is hoping to pinpoint chemicals in the pregnant mothers' blood that might be associated with a greater risk of breast cancer in their daughters, more than 50 years after they were born.

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