Study: Prenatal exposure to the pesticide DDT and breast cancer risk

RESEARCH SUMMARY

Study background:  

Previous research found no link between midlife DDT exposure and breast cancer. However, a link may still exist—exposure to DDT might only be significant when exposed at a certain age or period in a person’s life. It’s important for scientists to study this association, because although banned in the United States, DDT is still widely used as a pesticide in Africa and Asia.  In the United States, many women who were exposed to DDT during its widespread use in the 1960s are alive today and could be at increased risk for breast cancer.      

Researchers of this study wanted to know:

Whether a mother’s exposure to DDT affected breast cancer risk in their female children.

Population(s) looked at in the study:

Participants in this study belonged to a well-studied group known as the Child Health and Development Studies Pregnancy Cohort, which was specifically designed to study the associations between prenatal exposures and health and development in parents and their children. The women gave blood samples throughout their pregnancies, which occurred between 1959-1967. Researchers continued to follow the 9,300 female births up to the age of 54. Of these women, 137 were diagnosed with breast cancer by the age of 52. To study the relationship between DDT and breast cancer, researchers compared DDT levels in the blood from the pregnant mothers of 137 women who were diagnosed with breast cancer to DDT levels in the blood from the pregnant mothers of 315 women without breast cancer who were matched in age (these women were the control group).

Study results:

Women who had high prenatal exposure of DDT had:

• an almost 4 times increased risk of developing breast cancer by age 52.
• a greater than 4 times increased risk of developing HER2-positive breast cancer by age 52.
• a greater than 4 times increased risk of developing a more advanced cancer by age 52.

The study had limitations. Because the entire study population was from Oakland, California, the results may not apply to people from other regions. Researchers cannot definitively conclude that prenatal exposure to DDT was the single factor that accounted for increased risk in the women with breast cancer, or if additional exposure after birth also affected breast cancer risk.  Nor could researchers conclude that DDT was the only agent that was present prenatally and resulted in increased cancer risk in these women—exposure to other environmental pathogens or pesticides may have also played a role.

Also, this study only noted whether women were diagnosed with breast cancer by age 52.  It did not mention at what ages the women developed cancer, so we do not know if early-onset cancer was involved. And this study only included women from the general population; it is not known how DDT affects people with mutations in BRCA or other genes that predispose people to develop breast cancer.

Conclusion:

Because DDT is still used in the world in accordance with World Health Organization guidelines, its effect on people is important to study. This research does show a potential link between high exposure to DDT in mothers and increased breast cancer risk in daughters; however, more work is needed to confirm this finding in a larger, more diverse population, and to determine additional information, including how DDT increases cancer risk, and whether other pesticides have similar effects.

A FORCE advisory board member noted that knowing which women from the 1960s were exposed to DDT in the womb would be difficult if not impossible, so it would also be difficult to use these findings for the benefit of this group of women.

Women concerned with prenatal exposures and breast cancer risk should remember that DDT is only one of several agents that are linked to increased breast cancer risk, including:

• polycyclic aromatic hydrocarbons (PAHs, a type of air pollutant)
• bisphenol A (BPA, used in the production of plastics)
• tobacco smoke