In studies conducted so far, chlordane has not been directly linked with causing breast cancer in either animals or in humans. The results of these studies have not been consistent. Two of these studies did not find significantly higher levels of chlordane or its breakdown products in the breast fat of women with breast cancer compared to women without the disease. It is difficult to make any definite conclusions from the very few small studies that have been conducted to date. Larger, more carefully designed studies are needed to further investigate whether higher body levels of chlordane and its breakdown products are associated with an increased risk of developing breast cancer.
Several studies involving larger groups of women are in progress.
A woman's lifetime exposure to estrogen has been linked to increased breast cancer risk. Estrogen is a female hormone that helps control the reproductive cycles and breast growth. There is a concern that synthetic chemicals that act like estrogen or cause other chemicals to act like estrogen may increase a woman's risk of developing breast cancer. In one laboratory experiment designed to test for a chemical's ability to act like estrogen, chlordane did not act like estrogen when it was tested alone. There is currently no evidence that chlordane can enhance the estrogen-like effects of other environmental pollutants.