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Suzanne M. Snedeker
Cornell University
PALS Slide #1
Text of Script
- Pieces of the Puzzle: Does Atrazine Affect the Risk of Cancer? by Suzanne M. Snedeker, Ph.D., Associate Director for Translational Research at the Cornell University Program on Breast Cancer and Environmental Risk Factors (BCERF)
- This module is part of PALS, the Pesticide Applied Learning Series.
- This module examines whether atrazine affects the risk of different cancers, including breast cancer. Information in this module comes from research studies. This includes studies of people exposed to atrazine and from studies using laboratory animals.
- It also includes information on situations where atrazine exposure may be a concern, and reviews information on atrazine levels in water supplies.
- This module recommends areas where more research is needed to provide additional information on the cancer risk of atrazine.
PALS Slide #2
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- Do environmental chemicals affect the risk of cancer?
- This is a question being asked by scientists, cancer advocates, educators, policy makers, and those exposed to environmental chemicals in their homes and workplaces.
- In 1995 the Cornell University Program on Breast Cancer and Environmental Risk Factors was founded because concerned citizens and policy makers wanted to know if there was a relationship between pesticides and higher than average breast cancer rates in many New York State counties.
- This new translational research program was launched to provide science-based information on environmental risk factors and cancer.
PALS Slide #3
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In this approach we:
- Address the relationships between environmental factors and cancer risk.
- Critically evaluate the current scientific evidence using a strength of evidence approach.
- Translate this science-based data into information individuals can use to expand their knowledge and reduce their risk of cancer.
- However, we do not always have clear answers. So, we also recommend promising avenues of new research to help clarify any uncertainties.
- In this module we will explore why consumers are concerned about pesticides and cancer risk. This will include learning more about how cancers, in this case, breast cancer develops. We will also explore the Environmental Protection Agency's cancer risk assessment of the herbicide atrazine and the types of exposures that may be of concern for both pesticide applicators and the general consumer.
- First, let's talk about breast cancer risk and ways pesticides can affect the risk of breast and other cancers.
PALS Slide #4
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- The American Cancer Society has estimated that in the year 2002, 203,500 new cases of breast cancer will be diagnosed in American women, and 1,500 new cases will be diagnosed in men.
- Over one-fifth of the women and one-third of the men diagnosed with breast cancer will die of the disease.
PALS Slide #5
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The puzzle of breast cancer
- Breast cancer is a very complex disease.
- There is no one single factor associated with causing the disease.
- Breast cancer develops over a long period of time. It can take 10 to 30 years for a normal cell to develop into a detectable tumor.
PALS Slide #6
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- How does breast cancer occur? The development of breast cancer is a long process that has many steps.
- Breast cancer occurs as a result of accumulating changes in key genes that control a cell's ability to divide, mature and die.
- These changes can result in an abnormal cancer cell that divides out of control and forms a tumor.
PALS Slide #7
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- As the tumor grows in size, it may invade surrounding or distant tissues.
- If cancer cells break off from the primary tumor they may travel to distant sites in the body, invading vital organs such as the brain, bone, liver or lung, and establish new tumors. When these vital organs fail, it can be fatal.
- That is why early detection and treatment are so important. It increases the chances of removing the tumor when it is small, before it has grown and invaded other tissues.
PALS Slide #8
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- What affects a person's risk of breast cancer? Breast cancer risk factors are like puzzle pieces. We know how some of the puzzle pieces fit together and affect risk. For other risk factors, we are just learning about the role they may play.
- Gender is the main factor that affects risk. Women have higher breast cancer rates than men.
- Advancing age, the age when a girl gets her first period, the age when a woman stops menstruating, a higher consumption of alcohol, and the use of hormone replacement therapy also affects breast cancer risk. These factors may increase exposure to certain reproductive hormones, such as estrogen and progesterone, which can stimulate breast cells to divide and grow.
- A dividing cell is more prone to making mistakes when copying its genetic material, leading to a higher rate of "by chance" or spontaneous mutations. A mutation can also be induced by an environmental chemical. Normally, our cells are very efficient at repairing these damaging mutations. However, a spontaneous or an induced mutation can be made permanent and be passed on to new daughter cells during cell division.
PALS Slide #9
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- A close relative with breast cancer (a mother, sister or grandmother), and having certain breast cancer susceptibility genes only accounts for five to seven percent of breast cancer risk. Therefore, most women who are diagnosed with breast cancer have no family history.
- The age when a woman has her first child also influences breast cancer risk. About 30% of breast cancer risk is explained by having a child late in life after 30 years of age, or never having children. Having children early in life causes immature breast cells to change and become resistant to the effects of cancer-causing chemicals.
- Other factors associated with an increased risk of breast cancer include certain types of benign breast disease, and exposure of the breast to ionizing radiation.
PALS Slide #10
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- For many other factors, we are just beginning to understand their role in breast cancer risk.
- A diet rich in fruits, vegetables and fiber may be associated with a lower risk of breast cancer. As was previously mentioned, a higher consumption of alcohol has been associated with more exposure to the hormone estrogen and a higher risk of breast cancer.
- Being overweight after menopause is associated with higher breast cancer risk. That is why regular exercise is important to help control body weight.
- There is concern that exposures to certain environmental chemicals may lead to a higher risk of breast cancer. This includes some types of dyes, flame retardants, solvents, passive cigarette smoke, certain pharmaceutical drugs and several pesticides.
PALS Slide #11
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- Why is there a concern among consumers that pesticides may play a role in cancer risk? There is concern because of the potential for exposure.
- We use pesticides :
- In agriculture to raise crops and livestock - In the home and garden to control weeds, structural insects and animal pests
- To control pests in recreational areas like golf courses, parks, playgrounds and athletic fields, and
- For large scale insect control against vector-borne diseases.
- The Environmental Protection Agency estimated that in 1997 nearly one billion pounds of pesticides were used in the United States alone. About 79% was used in agriculture, 14% for industrial, commercial and governmental use, and seven percent in the home and garden.
PALS Slide #12
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- Researchers have identified several ways that pesticides may affect breast cancer risk.
- Some pesticides may act as "complete" carcinogens. A complete carcinogen is capable of taking a normal cell through the entire multi-step process to form an invasive tumor. Only a few pesticides have been identified as "complete" carcinogens.
- Another way is to act as a tumor promoter. A tumor promoter may give an existing tumor a growth advantage, promoting its further growth and development.
- The insecticide DDT has been identified as a tumor promoter in laboratory animals. When given with or after a known cancer-causing chemical (called a carcinogen), a tumor promoter can cause a higher number or earlier appearance of breast tumors than if only the cancer-causing chemical is given.
PALS Slide #13
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- Other pesticides may affect breast cancer risk by acting as "endocrine disruptors," also called "hormonally active agents." These chemicals may mimic a known hormone, such as estrogen, or in another way affect the formation or breakdown of hormones that regulate cell division.
- Pesticides that mimic the effect of estrogen may be able to support the growth of an existing estrogen-dependent breast tumor. We know that over half of all breast tumors depend on estrogen for growth.
- Scientists are only starting to identify which pesticides are endocrine disruptors, including estrogen mimics. The insecticides DDT and methoxychlor are weak estrogen mimics. The 1996 Food Quality and Protection Act mandates that the Environmental Protection Agency develop screening tests to identify which pesticides act as endocrine disruptors.
PALS Slide #14
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- What is the evidence that certain pesticides affect cancer risk?
- The Environmental Protection Agency has been evaluating the cancer risk of atrazine since the 1980s.
PALS Slide #15
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- Atrazine is one of the most widely used herbicides in the United States.
- It was first registered for use in 1959.
- Up to 77 million pounds of atrazine, as the active ingredient, were used per year during the 1990s.
PALS Slide #16
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- About 98% of atrazine usage is on agricultural crops.
- Its primary use is as a pre- and post-emergent herbicide on field and sweet corn, especially in the Midwestern corn-belt states.
- According to the US Department of Agriculture, about 69% of the corn crop was treated with atrazine in 1998 and about 82% of sorghum was treated with atrazine.
- Atrazine is also used for weed control on sugarcane fields.
PALS Slide #17
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- It is used to a lesser extent for weed control on other crops including winter wheat, guava and macadamia nuts, and on hay for animal feed and fodder, and to control weeds on fallow land.
- It is also used to control weeds on Christmas tree farms.
PALS Slide #18
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- Non-agricultural uses only make up about two percent of atrazine's usage. This includes weed control:
- On turf, including golf courses and home lawn care in the Southeastern US. Atrazine is used for weed control on St. Augustine and Bermuda grass.
- And on roadways and right-of-ways in some Midwestern and Western states.
PALS Slide #19
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- Application rates for atrazine vary according to its use.
- In agriculture, the average field corn application rate is one pound of active ingredient per acre, while the maximum rate of application is two and a half pounds of active ingredient per acre.
- For sugarcane, the maximum application rate is ten pounds per acre, while on turf in the Southeastern US, application rates are usually two pounds or less per acre.
- Always refer to the product label for correct application rates.
PALS Slide #20
Text of Script
- Is there evidence that atrazine exposure can affect breast cancer risk in women exposed to this herbicide? There are few studies of women that have attempted to answer this question. Unfortunately, there are no well-controlled human studies that have evaluated breast cancer risk in women exposed to atrazine compared to women not exposed to this herbicide.
- Two "ecological" studies have been conducted in Kentucky. Ecological studies approximate exposures of a population within a certain geographic area rather than evaluating exposures of individuals.
- In the first study researchers found higher breast cancer rates in women living in counties with:
- A higher use of corn herbicides and
- Higher levels of triazine herbicides in water supplies.
- This study did not estimate actual exposures to atrazine, but used surrogate measures, like number of acres of corn grown, to estimate atrazine exposure.
- This may have introduced inaccuracies, since many herbicides besides atrazine are used as corn herbicides.
Disclaimer and Reproduction Information: Information in NASD does not represent NIOSH policy. Information included in NASD appears by permission of the author and/or copyright holder. More
NASD Review: 08/2004
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