Cancer

Regulatory agencies require extensive testing for human safety, including cancer, of each pesticide before market approval.

Cancer is an increasingly common disease due in large part to aging, changing lifestyles and improved diagnostics. Scientists have identified modifiable risk factors, such as smoking, alcohol, unhealthy diet, obesity, insufficient physical activity and infections as contributing to the risk of certain cancers. Regulatory agencies require extensive testing for human safety, including cancer, of each pesticide.

Definitions

The term “cancer” represents a group of diseases marked by unchecked growth of abnormal cells. Cancer is not a single disease. Different cancer types are indicated by the cell type and the part of the body first affected. The different types also have differing disease profiles and risk factors. For example, colon cancer is more common in individuals who are older than 50 years of age and it is linked to smoking, obesity and lack of exercise. In contrast, smoking and obesity have not been strongly associated with prostate cancer, but the risk of this cancer also increases with age. Therefore, among different types of cancer there are often significant differences in trends over time, between geographical regions, and across ages and gender.

Regulatory agencies require extensive testing for human safety, including cancer, of each pesticide.

The term “pesticides” is also a generic term, referring to a wide group of products, both synthetic and natural, that by definition are harmful to a plant, insect, fungus or rodent. Today, for a pesticide to be legally sold and used across the globe, specific and stringent tests are required to evaluate the potential for it to cause cancer.

Cancer in Society

Cancer is strongly associated with age and the increase in people reaching old age has resulted in greater incidence of cancer. The numbers of new cases and resulting deaths vary from region to region. In the United States and European Union, about one in four deaths is attributed to cancer. The frequency of cancer and other non-communicable diseases is increasing in particular in lower income regions of the world because of reduction in communicable diseases, conditions arising during pregnancy and childbirth, and nutritional deficiencies. The World Health Organization (WHO) predicts that the number of new cases of cancer will rise by about 70 percent over the next two decades.

The role of pesticides in agriculture is to provide higher quantity and quality of fruits and vegetables – consumption of which is recommended by all authorities to reduce the risk of many cancers and other important diseases.

Collectively, experts (e.g., WHO, Cancer Research U.K., U.S. National Cancer Institute) agree that in addition to aging, the leading behavioral risk factors for cancer are smoking, alcohol, unhealthy diet, obesity and insufficient physical activity. Infectious agents, such as human papillomavirus and hepatitis B and C viruses, are also important contributors to certain types of cancer.

The global fight against cancer is directed at reducing these behaviors and infections. This is demonstrated by regional goals, for example, of the WHO’s Pan American Health Organization and African Regional Office to promote a healthy diet, physical activity, tobacco control and reduction of alcohol consumption. Exploring the possible association of pesticide exposure and cancer is not a stated priority for these organizations. On the contrary, the role of pesticides in agriculture is to provide higher quantity and quality of fruits and vegetables – consumption of which is recommended by all authorities to reduce the risk of many cancers and other important diseases.

Classification

Pesticides are evaluated to determine their safety to humans, the environment and non-target species. Extensive testing is done on each pesticide to determine if it can damage cells or lead to tumors in laboratory animals. These tests are conducted at levels of exposures that farm workers or people at large would never ordinarily experience.

Regulatory bodies, such as the European Food Safety Authority (EFSA), United States Environmental Protection Agency and Australian Pesticides and Veterinary Medicines Authority, evaluate the evidence for specific pesticides and cancer. These agencies will classify the strength of the evidence using a sliding scale, such as carcinogenic, likely, suggestive, inadequate or not likely. The resulting recommendations about using a pesticide safely and guidelines for the sale, volume and use patterns will be determined from these classifications. Personal exposures to farm workers can be further reduced by wearing protective clothing and following label directions.

Very large studies of farmers (and people with access to pesticides) are underway in the U.S. and France. Results to date from these studies have shown that farmers tend to be healthier and have less cancer overall than comparison populations.

The International Agency for Research on Cancer (IARC), while not a regulatory agency, also evaluates and classifies specific chemicals, including certain pesticides. The IARC has classified only two pesticides, lindane and arsenic, as “carcinogenic to humans.” Its other classifications of “probably carcinogenic to humans” and “possibly carcinogenic to humans” indicate inconsistency of the evidence. This has been discussed with the herbicide glyphosate, for example, where an epidemiological study of more than 50,000 farmers showed no statistically significant increase on any cancer.1

Evidence in Human Studies

To study causes of cancer, researchers look among groups of people that either have the same cancer, such as brain cancer, or groups of people that have a similar lifestyle or exposure, such as smoking. Some occupational groups, such as farmers, are often studied because they use a variety of pesticides in their jobs. Investigators compare rates of specific cancer(s) in one group to the rest of the population. These studies also try to determine if a specific pesticide is used more frequently in the group with cancer. These statistical exercises may link a cancer with farming or a pesticide, but repeated studies are needed to confirm the initial associations, which rarely occurs. Very large studies of farmers (and people with access to pesticides) are underway in the U.S. and France. Results to date from these studies have shown that farmers tend to be healthier and have less cancer overall than comparison populations.2,3,4,5,6

Studies of pesticides are ongoing to evaluate if exposure to specific ones is associated with cancer.

The EFSA reviewed 164 publications on pesticide exposure and cancer.4 It concluded that while some studies showed associations between occupational exposure to pesticides and a specific cancer, such as for lymphoma, leukemia and prostate cancer, other studies did not. The EFSA reviewers recommended additional studies to evaluate childhood exposures and leukemia before drawing firm conclusions.

With the possible exception of a few agents of mainly historical interest that are no longer in use, pesticides are not an established cause of cancer. Studies continue to be conducted in humans, animals (“in vivo”) and cellular systems (“in vitro”) to better understand the disease progression and ultimately, the cause of specific cancers. Similarly, studies of pesticides are ongoing to evaluate if exposure to specific ones is associated with cancer.


1 Andreotti G, Koutros S, Hofmann JN, Sandler DP, Lubin JH, Lynch CF, Lerro CC, De Roos AJ, Parks CG, Alavanja MC, Silverman DT and Beane Freeman LE. 2017. Glyphosate use and cancer incidence in the Agricultural Health Study. J Natl Cancer Inst. 2017 Nov 9. doi: 10.1093/jnci/djx233. [Epub ahead of print]
2 Frost G, Brown T, Harding AH. 2011. Mortality and cancer incidence among British agricultural pesticide users. Occup Med (Lond) 61(5), 303-310.
3 Koutros S, Alavanja MC, Lubin JH, Sandler DP, Hoppin JA, Lynch CF, Knott C, Blair A, Freeman LE. 2010. An update of cancer incidence in the Agricultural Health Study. J Occup Environ Med 52(11), 1098-1105.
4 Levêque-Morlais N, Tual S, Clin B, Adjemian A, Baldi I, Lebailly P. 2015. The AGRIculture and CANcer (AGRICAN) cohort study: enrollment and causes of death for the 2005-2009 period. Int Arch Occup Environ Health 88(1), 61-73.
5 Ntzani EE, Ntritsos GMC, Evangelou E, Tzoulaki I. 2013. Literature review on epidemiological studies linking exposure to pesticides and health effects. EFSA Supporting Publications 10(10), 159 pp.
6 Waggoner JK, Kullman GJ, Henneberger PK, Umbach DM, Blair A, Alavanja MC, Kamel F, Lynch CF, Knott C, London SJ, Hines CJ, Thomas KW, Sandler DP, Lubin JH, Beane Freeman LE, Hoppin JA. 2011. Mortality in the agricultural health study, 1993-2007. Am J Epidemiol 173(1), 71-83.

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