The results of a new study suggest that high levels of specific PCBs may be linked to breast cancer.

Some persistent environmental contaminants that accumulate in the body of women with age and are similar in structure to dioxin may be a risk factor for breast cancer.

The findings also highlight the importance of additional research on the possible link between environmental contaminants that can mimic hormones or alter hormone metabolism and the risk of breast cancer.

PCBs, or polychlorinated biphenyls, are a class of chemicals with a variety of industrial and commercial applications. Because of concerns about the health effects of the chemicals, PCBs were banned in the US and Canada two decades ago. The chemicals still linger in the environment and are present in the food chain, particularly in fatty foods.

During the past decade, there have been many studies of the possible link between exposure to PCBs and an increased risk of breast cancer. Most studies did not detect a link between high levels of the chemicals and breast cancer, but most of the studies looked at overall levels of PCBs, not individual chemicals.

Researchers examined the relationship between breast cancer risk and 14 individual PCBs in 314 women with breast cancer and a "control" group of 523 healthy women.

Levels of two PCBs -- PCB 118 and PCB 156 -- were linked to a 60% to 80% greater risk of breast cancer, the researchers report. This relationship was more pronounced in premenopausal women.

The study also found that women with high levels of a combination of three PCBs that mimic the cancer-causing chemical dioxin -- PCBs 105, 118 and 156 -- were about twice as likely to have breast cancer. These chemicals are known as mono-ortho PCBs. This risk was also greater in premenopausal women.

The results may indicate a relation between dioxin-like compounds and breast cancer risk. The study is the second large study to suggest a link between mono-ortho PCBs and breast cancer.

American Journal of Epidemiology April 1, 2002;155:629-635