Last Updated: 2003-04-25 17:05:54 -0400 (Reuters Health)
NEW YORK (Reuters Health) - Women with breast cancer may be more likely to have pesticide residues in their blood, a new study from Belgium suggests.
In the study, women with breast cancer were more likely to have residues of the chemicals DDT and HCB in their blood than women who did not have cancer.
"These results add to the growing evidence that certain persistent pollutants may occur in higher concentrations in blood samples from breast cancer patients than controls," writes a team led by Dr. Charles Charlier of Sart Tilman Hospital in Liege, Belgium.
Nonetheless, the findings do not prove that exposure to the chemicals causes breast cancer.
In fact, a 2001 analysis of five studies involving more than 1,400 people with breast cancer and more than 1,600 people without cancer living in New York, Maryland and Connecticut found no association between DDT and chemicals called PCBs and breast cancer.
Charlier's team calls for more research on the topic, noting that the development of cancer "is a multifactorial event, and it is important to try to clarify the role of chemicals in cancer development."
These chemicals, which can build up in fatty tissue and blood, were used in the U.S. until the 1970s. DDT, a pesticide, was banned in 1972 after it was found to cause egg shell thinning in wild birds, and HCB was widely used as a pesticide to protect the seeds of agricultural plants against fungus until 1965. Currently, HCB is not used commercially in the United States.
Studies have shown that these and other environmental pollutants mimic the effects of estrogen by stimulating the growth of precancerous and cancerous breast cells in test tubes.
But the effects of exposure to the chemicals in humans have remained unclear, with some studies finding an association among women with breast cancer, while others have not.
Charlier's group tested for the presence of DDT and HCB in blood samples from 159 women with breast cancer and 250 healthy women.
The study, reported in the journal Occupational and Environmental Medicine, found that women with breast cancer were more likely to show signs of pesticide exposure. Twenty-four percent of the healthy women had no detectable levels of the pesticides in their blood compared to only 2.5 percent of the women who had breast cancer.
Specifically, women with breast cancer had concentrations of DDT and HCB in their blood that were more than twice as high as those measured in healthy women.
Although some breast tumors are sensitive to the effects of estrogen and others are not, DDT and HCB levels were not related to estrogen sensitivity.
The authors conclude that more research is needed, including how women might be exposed to these chemicals.

Occupational and Environmental Medicine 2003;60:348-351.