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Pesticides and Breast Cancer

by aseligmann — last modified Oct 01, 2010 12:00 AM

Every October during National Breast Cancer Awareness Month, women are educated about the importance of early detection through regular screening. Early diagnosis of breast cancer increases a woman's chances of surviving breast cancer. But what causes breast cancer? Can it be prevented?

Every October during National Breast Cancer Awareness Month, women are educated about the importance of early detection through regular screening. Early diagnosis of breast cancer increases a woman's chances of surviving breast cancer. But what causes breast cancer? Can it be prevented?

Risk Factors For Breast Cancer

Women have no control over some breast cancer risk factors such as family history and getting older. The American Cancer Society says, "It could be that a woman of average risk for breast cancer might lower her risk somewhat by changing those risk factors that can be changed. These include giving birth to several children and breast-feeding them for several months, not drinking alcohol, exercising regularly, and staying slim."

Do Chemical Pollutants Cause Breast Cancer?

According to the American Cancer Society, the causes of most breast cancer are not known. What about chemicals in our environment? The ACS says "At this time, research does not show a clear link between breast cancer risk and environmental pollutants, such as pesticides and PCBs."

In fact, it is not easy to figure out what chemicals might be linked to breast cancer. Breast cancer might show up years after a woman was exposed to chemicals. Exposure can also occur over a period of time. In addition to this, we are all exposed to many different chemicals. It can be difficult to identify 'culprits' under such circumstances.

Pesticides Linked To Breast Cancer

Pesticides are one component of the many chemicals that we are exposed to in our everyday lives. The results of studies on pesticides and breast cancer have been mixed. Four recent studies found that exposure to certain pesticides were associated with a higher risk of breast cancer.


Estrogen - the female hormone - is a risk factor for breast cancer. Breast cancer risk is related to a woman's life-long exposure to her own natural estrogen. For example, a woman is more at risk if her menstrual periods begin and an early age, and she experiences late menopause.

Some chemicals, including some pesticides, can act like estrogen in the body. Scientists have wondered if these chemicals might also be linked to breast cancer.

DDT and Other Organochorines May Mimic Estrogen

DDT, the insecticide banned for pushing bald eagles towards extinction, belongs to a chemical family called organochlorines. Some organochlorines are known to affect the hormone system. Once organochlorines enter our bodies, they are stored in our fat.

For breast cancer studies, researchers first measure how much of these chemicals are in women's fat. Then they compare the amounts found in women who have breast cancer to the amounts found in women who don't have breast cancer. A number of older health surveys used this method to look for a connection between DDT and breast cancer, but most of these studies did not find a strong link.

Most organochlorine insecticides have not been used in the U.S. for many years, but they are still widespread in the environment - in soil, in food, and in our bodies.

Study Links Chemical in Head Lice Shampoo to Breast Cancer

In a study published in 2004, scientists from Spain tested women's fat to examine a number of organochlorine insecticides. The results showed that women who had aldrin and lindane in their bodies were more likely to have breast cancer.

All uses of lindane were cancelled by the Environmental Protection Agency in August 2006. However the Food and Drug Administration still permits lindane in head lice shampoo.

Insecticide Affects the Risk of Breast Cancer and Survival

Danish scientists were able to look at residues of organochlorines in blood serum. Denmark had started a health study of women in the mid-70s. They collected samples of blood from the women and stored the samples for later research. Seventeen years later, the researchers tested the blood samples for organochlorine insecticides.

Comparing women with breast cancer to those without, they found that dieldrin was associated with an increased risk of breast cancer. A subsequent study showed that dieldrin was also linked to lower survival rates for these women.


Two California studies published just this year (2006), investigated breast cancer in Hispanic women farmworkers. Of female farmworkers in California, 80% are Hispanic.

As a heavily agricultural state, California leads the nation in pesticide use. Farmworkers are constantly exposed to pesticides -- insecticides, herbicides, and fungicides -- through their work.

Top Pesticides and Different Crops Examined

One study compared the farmworker women who were diagnosed with breast cancer from 1998-2001 to a group of farmworker women who were cancer-free. Researchers looked for risks associated with different crops and risks associated with the top chemicals that had been used. The only crop associated with breast cancer was mushrooms -- although the reasons were not clear.

Of the insecticides, malathion and chlordane were associated with increased breast cancer risk. Malathion is used in home garden products, agriculture, and mosquito control. Chlordane was banned in 1983. Among its many uses, it was applied around homes to control termites.

For the first time, the herbicide 2,4-D was linked to breast cancer. 2,4-D is widely used in lawn products and agriculture.

Study of Suspected Chemicals -- Organochlorines and Triazines

In the second farmworker study, researchers focused on two families of chemicals - the organochlorine insecticides and the triazine herbicides that are also known to disrupt the hormone system.

Using years of data found in California pesticide use reports, they determined how much of these chemicals were used each year in each California county. This data was compared to the work history of the farmworker women -- the years and the places where the women worked. The triazine herbicides atrazine and simazine were not associated with breast cancer.

Two organochlorine insecticides, methoxychlor and toxaphene, increased the risk of breast cancer. Both of these insecticides are now banned.


These studies do not establish pesticides as a cause of breast cancer. (Think about how long it took for smoking to be established as a cause of lung cancer!) But they do show that chemicals can be linked to the risk of breast cancer. Studies like these help us understand the consequences of deliberately adding toxic chemicals to the environment.

  • American Cancer Society. 2006. Overview: Breast cancer. What causes breast cancer?
  • Hoyer AP, et al. 1998. Organochlorine exposure and risk of breast cancer. Lancet. 352(9143):1816-1820
  • Hoyer AP, et al. 2000. Organochlorine exposure and breast cancer survival. Journal of Clinical Epidemiology 53(3):323-330.
  • Ibarluzea, JM et al. 2004. Breast cancer risk and the combined effect of environmental estrogens. Cancer Causes & Control 15(6):591-600.
  • Mills, PK and R Yang. 2005. Breast cancer risk in Hispanic agricultural workers in California. International Journal of Occupational Environvironmental Health 11(2):123-131.
  • Mills, PK and R Yang. 2006. Regression analysis of pesticide use and breast cancer incidence in California Latinas. Journal of Environmental Health 68(6):15-22.
  • Mitra, AK, FS Faruque and AL Avis. 2004. Breast cancer and environmental risks: where is the link? Journal of Environmental Health 66(7):24-32,40