Susan Lydon, a Bay Area author and journalist, never forgot the DDT fog trucks that rumbled through the Long Island, New York, neighborhood where she grew up.

She was her block's fastest kid. The mist was cool. The trucks slow. Her speed allowed her to stay longer than any other pals in that comforting, pesticide-laced mist the sprayers left in their wake.

Lydon died of breast cancer at age 61 in 2005, going to her deathbed certain those carefree runs decades ago sealed her fate.

Her concern, it appears now, was justified.

A breakthrough study of Oakland women suggests exposure early in life to DDT significantly increases a woman's chances of developing breast cancer decades later, according to a new study published last week in the online edition of the journal Environmental Health Perspectives.

The findings bolster the controversial notion that exposure to low doses of hormonally active compounds at critical developmental stages — in this case, as the breast is developing — load the gun, so to speak, priming the body to develop cancer years later.

It also makes clear the final chapter of DDT's legacy is not yet written. The young girls most heavily exposed to the pesticide — women born in the late 1950s and early 1960s, when use of the pesticide peaked in the United States — have not yet reached age 50, let alone the age of greatest breast cancer risk, typically sometime after menopause and around age 60.

The findings further suggest society is destined to relearn the lesson of DDT many times over. Myriad synthetic chemicals in our environment today interact with our bodies, with unknown consequences. Government regulators have little power to take precautionary action against compounds that appear problematic.

Reports like this, said Barbara Brenner, executive director of San Francisco-based Breast Cancer Action, show the fallacy of that approach.

"We have to start paying very close attention to what we put in our environment," she said. "This is an example of doing something to our environment where we did not understand the long-term consequences. I don't know how many times this story has to be told."

The study probed a unique database of some 15,000 Kaiser Permanente Health Plan members who participated in a longitudinal study tracking their health over decades.

Researchers with the Berkeley-based Public Health Institute selected 129 women within that study who developed breast cancer before age 50, then analyzed their archived blood samples taken between 1959 and 1967, while they were much younger.

Every sample from a woman with cancer was matched as a control with a sample from a woman of the same age without cancer.

Researchers found women who developed cancer later in life had far higher concentrations of DDT in their blood as youths.

More significantly, women who were 14 years old or older in 1945, when DDT first hit the market, saw no increased breast cancer rates, suggesting exposure while the breast is developing is critical.

The study has its limits. Researchers don't know about other known risk factors that may have predisposed the women toward cancer. They don't know when the women were exposed to DDT. And the study size is small.

For those who, like Lydon, have memories of chasing DDT sprayers as a child, researchers involved in the study preached caution against drawing any firm conclusions.

"I don't think it's just early life exposures," said Mary Wolff, a professor of oncology at Mount Sinai School of Medicine and a report co-author. "Most cancers are an accumulation of a lot of factors."

Even among women most at risk — those with the so-called "breast cancer gene" — 30 percent live to age 70 and beyond without cancer, for reasons unknown, Wolff said. "It's a complex disease even when we know one of the biggest risk factors.

DDT, or dichloro diphenyl trichloroethane, was banned in the United States in 1972 amid concerns it was concentrating in the food chain and killing off bald eagles and other raptors.

But the report goes far beyond the pesticide. It indicts widely held ideas and common practices concerning minute amounts of chemicals ubiquitous in our environment.

"The work that needs to be done to identify whether there are environmental risk factors (with any particular compound) is very complicated," said Barbara Cohn, a senior researcher at the Health Institute and the report's lead author. "But it's very important. We need to look deeply at that."

The report suggests, for instance, that society is heading down the same path with atrazine, one of the world's most widely applied pesticides, said Breast Cancer Action's Brenner.

The most cutting-edge drugs in the fight against breast cancer are known as aromatase inhibitors. Post-menopausal women only produce estrogen in their adrenal glands, using the enzyme aromatase to convert the glands' androgen hormones to estrogen. Because estrogen stimulates some breast cancers, doctors attempt to curb cancer growth by blocking the body's production of aromatase.

Atrazine is an aromatase stimulator.

Despite this and other concerns about the pesticide's impact on wildlife, federal regulators say the science is too inconclusive to curb its use.

"We start using chemicals as if the only thing they're going to affect is the plant," Brenner said. "We have to start doing business a different way."

Equally worrisome, the authors say, is that many of the women most heavily exposed to DDT have not yet reached age 50. DDT production peaked in the United States in 1965, and while most studies to date have concluded such exposure wasn't meaningful, this new evidence suggests those assurances may be premature.

The most strongly affected women — those exposed when young — are just now reaching age 50.

Said Cohn: "It's a caution that maybe there might be other types of evidence that need to be considered before that conclusion can be reached."

Contact Douglas Fischer at dfischer@angnewspapers.com or at (510) 208-6425.