5 August 2018

One in 15 Million: Cancer Risk Unlikely Related to Pesticide Exposure

Carol J. Burns, MPH, PhD

Burns Epidemiology Consulting

Does this dress make me look fat? This is the age-old question that every woman asks and no husband should ever answer. This year, as I look at my summer wardrobe, I’m asking a new question. Does this shirt hide my scar? In 2016, I had my thyroid removed and joined the estimated 1.6 million Americans diagnosed with cancer last year. Seemingly, everyone in my social circle has just been diagnosed or knows someone with a new diagnosis. I wonder, is cancer on the rise? Is it, my friends ask, due to exposure to pesticides? As a trained epidemiologist, I want to know if the answers are real or perceived.

Fortunately, there are excellent resources on cancer. For example, the American Cancer Society annually publishes statistics for the United States. Cancer Research UK provides informative sections on causes and controversies. The World Health Organization provides estimates for major types of cancer by region and for 184 countries. From these websites, several points about cancer are clear:

  • Cancer is not a single disease and each subtype has different causes and risk factors.
  • It is essential to distinguish between cancer mortality (deaths due to cancer) and cancer incidence (rate of newly diagnosed cases). Each provides important information and can be impacted by screening practices, treatment and health care systems.
  • A high proportion of cancer cases worldwide are due to certain behavioral factors: smoking, alcohol, unhealthy diet, obesity and insufficient physical activity. Other factors such as age, sex and family history are not changeable.

Incidence and Diagnosis

This brings me to my first question. Is cancer really on the rise? Yes and no. In the United States1 and Europe,2 the incidence of cancer is stabilizing, albeit at a high level. American incidence seemed to peak in the 1990s, partly due to declining smoking habits. My type of cancer, thyroid cancer, is still increasing. Cancer experts attribute this to improved diagnostic tools and early detection.1 In other words, doctors are finding (and treating) cancer that might have been unnoticed in my parent’s generation.

Major cancer organizations … list risk factors for thyroid cancer as being a woman of middle age (40s and 50s), having a family history of thyroid cancer, history of goiter or thyroid nodules, low iodine in the diet and obesity, with no mention of pesticides.

Globally, the number of diagnosed cases of cancer is increasing. For better or worse, cancer incidence tends to be highest in more developed countries and regions. Since one of the main risk factors for cancer is older age, as a society reduces infant mortality and vaccine-preventable diseases, the population demographics change. Diseases of older age, such as cancer and heart disease, become more common. Furthermore, as lesser developed regions become more affluent, their citizens often adopt unhealthy lifestyles, such as poor diet and physical inactivity, which are also risk factors for cancer.

But overall, cancer mortality is declining in the United States and many other nations. There are wide variations by country and cancer type, which reflect early screening and advancements in treatment.

Pesticides and Cancer

The second question, could my cancer be triggered by to exposure to pesticides? Since the thyroid is part of the endocrine system, advocates of the endocrine disruption theory include thyroid cancer on their watch list. However, this is not likely. I investigated the evidence in three areas:

  • What is known about causes and risk factors for thyroid cancer?
  • Are persons with highest exposure to pesticide more likely to develop thyroid cancer than persons with no exposure?
  • What is my personal risk profile for thyroid cancer?

Very large studies of farmers (and other people exposed to pesticides) have shown that they tend to be healthier and have less cancer overall than comparison populations.

First, major cancer organizations, such as those above, list risk factors for thyroid cancer as being a woman of middle age (40s and 50s), having a family history of thyroid cancer, history of goiter or thyroid nodules, low iodine in the diet and obesity, with no mention of pesticides.

Secondly, very large studies of farmers (and other people exposed to pesticides) have shown that they tend to be healthier and have less cancer overall than comparison populations.3 4 5 6 As an example, the U.S. National Cancer Institute’s Agricultural Health Study reported lower rates of total cancer and no excess thyroid cancer among more than 80,000 private and commercial applicators and their spouses.7 Since the rest of the population has much lower and infrequent contact with pesticides, it is unlikely that cancer is related to pesticide exposure.

Third, regarding my risk of thyroid cancer, I’m in the category of well-educated, well-insured and well-fed women with a perceptive doctor able to detect nodules.8,9,10 In summary, the evidence doesn’t suggest that cancer, and certainly not my cancer, is related to pesticides.

As an epidemiologist, I am trained to look at information in populations and for patterns in groups of people, not individuals. This can be frustrating on a personal level. There isn’t a statistic or analytical test that can answer why me? Why did I get cancer? On the other hand, knowing about the different subtypes of cancer and the risk factors for each can guide my lifestyle choices to reduce many diseases, not just cancer.

For me, rather than being anxious about the etiology, I am relieved with my prognosis. Because of the early diagnosis, prompt removal and treatment, my scar is only skin deep. I do plan on exercising more, eating better and planting more flowers this summer. I will still ask my husband about how I look. However, I’ve decided to be proud of my scar. I can tell strangers that I am one in 15 million: that is, one of 15 million Americans1 with a history of cancer.

Carol J. Burns, M.P.H., Ph.D., F.A.C.E., is president of Burns Epidemiology Consulting, LLC in Sanford, Mich. She is a Fellow of the American College of Epidemiology.

1 American Cancer Society. Cancer Facts & Figures 2017. Atlanta: American Cancer Society.

2 European Network of Cancer Registries. ENCR Cancer Factsheets – new series. http://encr.eu/index.php/publications/factsheets

3 Waggoner JK, Kullman GJ, Henneberger PK, et al. 2011. Mortality in the agricultural health study, 1993-2007. Am J Epidemiol. 173(1):71-83.

4 Ntzani EE, Ntritsos G, M C, Evangelou E, Tzoulaki I. 2013. Literature review on epidemiological studies linking exposure to pesticides and health effects. EFSA Supporting Publications. 10(10):159 pp.

5 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.

6 Frost G, Brown T, Harding AH. 2011. Mortality and cancer incidence among British agricultural pesticide users. Occup Med (Lond). 61(5):303-310.

7 Koutros S, Alavanja MC, Lubin JH, et al. 2010. An update of cancer incidence in the Agricultural Health Study. J Occup Environ Med. 52(11):1098-1105.

8 Kitahara CM, McClullough ML, Franceschi S, et al. 2016. Anthropometric Factors and Thyroid Cancer Risk by Histological Subtype: Pooled Analysis of 22 Prospective Studies. Thyroid. 26:306-18 doi: 10.1089/thy.2015.0319.

9 Sprague BL, Warren-Andersen S, Trentham-Dietz A.  2008. Thyroid cancer incidence and socioeconomic indicators of health care access. Cancer Causes Control.Aug;19(6):585-93. doi: 10.1007/s10552-008-9122-0.

10 Schmid D, Ricci C, Behrens G, Leitzmann MF. 2015. Adiposity and risk of thyroid cancer: a systematic review and meta-analysis. Obes Rev. Dec;16(12):1042-54. doi: 10.1111/obr.12321.

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