However, because relatively few women were involved, the study is prone to statistical weakness, which may mean the result is partly attributable to chance, Stellman said.
Terry agreed: "Certainly if you have a larger study, the estimates you get are more stable. No one study can be definitive. It would be good to try to replicate the finding in another population of girls who were highly exposed."
For The Record
Los Angeles Times Thursday, October 04, 2007 Home Edition Main News Part A Page 2 National Desk 1 inches; 51 words Type of Material: Correction
DDT and cancer: An article in Sunday's Section A about the link between DDT and breast cancer identified the researchers as coming from UC Berkeley's Child Health and Development Studies. The project was part of the university until 1986 but is now administered by the nonprofit Public Health Institute in Berkeley.
But it is rare to find blood stored for 40 years, so replication would be difficult.
Exposure to DDT for the Bay Area women was probably no more extensive than elsewhere in the country at the time. Most of the 129 women did not live on farms, so they would have been exposed through food or urban spraying.
DDT is prohibited today in most of the world, though it is used in small volumes in some malaria-plagued African nations.
But virtually everyone on the planet still carries residue because the pesticide persists in the environment and in tissues, breaking down slowly.
Many environmental toxicologists and epidemiologists have in recent years altered their thinking about toxic exposures. They used to focus on lifetime exposure. But now they suspect that chemicals may activate genes or damage DNA in the womb or during early childhood, resulting in diseases decades later.
Other evidence suggests that breast cancer can be triggered early in life. In lab animals, prenatal doses of chemicals can trigger cancerous cells in fetal mammary glands. Also, Japanese females who were younger than 20 in 1945 developed the highest breast cancer rates among those exposed to radiation from the atomic bombs.
The new study does not indicate the age of greatest vulnerability to exposure. Breast development is most critical in the womb and at puberty.
Whether or not DDT promotes breast cancer, there are many other risk factors, including alcohol consumption, hormone therapy and age at menstruation.
The known risk factors are believed responsible for up to half of cases.
"We truly believe it's not one exposure that's going to determine whether you get breast cancer or don't get breast cancer," Reynolds said.
"While it's true that our generation may be more at risk from those exposures, there are a whole lot of other things involved too."
marla.cone@latimes.com
