WEDNESDAY, April 23, 2003 (HealthDayNews) -- A new study has found that women with breast cancer were more than five times as likely to have traces of the pesticide DDT in their blood than women without breast cancer.
These women were more than nine times as likely to have a residue of the fungicide hexachlorobenzene (HCB), the Belgian study says.
The findings, which appear in the May issue of Occupational and Environmental Medicine, do not prove conclusively that DDT or HCB actually cause breast cancer. It's also not clear if they add to the case implicating pesticides in human cancer.
"I don't think that this research would shake the ground in the environmental research field," says Dwight E. Randle, director of the award and research grant program at the Susan G. Komen Breast Cancer Foundation in Dallas. "Other studies have gone back and forth. If you look at the research that's been done in this area as a whole, the bottom line is that we don't know yet."
The search for a definitive answer is fueled largely by a desire to explain why breast cancer has been on the rise during the last 100 years or so.
"When we look at the increase in the incidence of breast cancer over the past century, it seems plausible that there's some environmental factor that's associated with this rise," says Dr. Carina Biggs, director of breast surgery at Maimonides Medical Center in New York City. "Whether that is an estrogenic pesticide or whether pesticides are only a small fraction of environmental influences is unclear."
DDT, or dichlorodiphenyltrichloroethane, was developed after World War II to eradicate insects that carried malaria, typhus, and other diseases as well as to protect crops. The U.S. Environmental Protection Agency (EPA) banned its use in 1972 after evidence suggested that it disrupted reproductive mechanisms in birds. The pesticide is also banned in Canada and Europe, according to the study authors, but is still used for mosquito control in developing countries. DDT can remain active in tissues for up to 50 years, say the study authors, and even today people ingest small quantities of the compound from dietary and other sources.
HCB was used during the same time period (1940s until the 1970s) on grain seeds such as wheat, according to the EPA. Although it is no longer used as a pesticide, it is formed inadvertently as a by-product in the production of other pesticides, chlorine, metal cans, and more.
DDT, HCB and other "environmental endocrine disrupters" mimic the action of certain hormones, including estrogen, in the body. Breast cancer, along with several other cancers, has a strong hormonal component, leading to suppositions that these compounds have contributed to the rise in breast cancer incidence.
That supposition led the authors of this study to look at 159 women with newly diagnosed breast cancer at a hospital in Liege, Belgium. All women were tested for levels of DDT and HCB in their blood before undergoing any treatment, including surgery, radiation, or chemotherapy.
The samples were compared with blood taken from a group of 250 healthy women who served as controls.
The women with breast cancer were more than five times as likely to have detectable levels of DDT as the healthy women and more than nine times as likely to have detectable levels of HCB.
Women who had estrogen-receptor-positive breast cancer did not have higher levels of DDT or HCB.
The findings are in keeping with what is already know about estrogen and breast cancer.
"Women who have estrogen withdrawn from them at an early part of life have a dramatically lower risk of breast cancer," says Dr. Jay Brooks, director of hematology/oncology at the Ochsner Clinic Foundation in Baton Rouge, La. "What we're beginning to realize is that anything that increases estrogen or estrogen-like compounds probably does increase the risk of a woman developing breast cancer."
Whether or not DDT and HCB can be included in that category is still a big unknown. "A lot of people are interested in giving a definitive answer to this question but that definitive series of studies hasn't been done yet," Randle says.
More information
For more on DDT exposure, visit the U.S. Centers for Disease Control and Prevention. The World Wildlife Federation has a fact sheet on HCB.
