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CANCER INCIDENCE IN THE AGRICULTURAL HEALTH STUDY
Citation:
Alavanja, M., D. Sandler, C. Lynch, C. Knott, J. H. Lubin, R. Tarone, K W. Thomas, M. Dosemeci, J. Barker, J. A. Hoppin, AND A. Blair. CANCER INCIDENCE IN THE AGRICULTURAL HEALTH STUDY. Presented at 2002 International State of Science Symposium on Agricultural Exposures and Cancer, Oxford, United Kingdom, November 19-22, 2002.
Impact/Purpose:
The primary goal of the AHS Pesticide Exposure Study (AHS/PES) is to measure exposure to applied pesticides for a subset of the cohort of private pesticide applicators and to provide data to evaluate exposure algorithms developed for exposure classification in the study cohort.
Description:
Despite low mortality and cancer incidence rates overall, farmers may experience excess risk of several cancers. These excesses have been observed in some, but not all, retrospective epidemiological studies of agricultural workers in several countries. Excess risk has been observed for cancers of the lymphatic and hematopoietic system, connective tissue, skin, brain, prostate, stomach and lips. Several of these tumors (brain, NHL, multiple myeloma, and prostate) are also increasing in the general population in many of these countries. This suggests that a common set of exposures may explain the higher rates in farmers and the rising rates in the general population. Farmers, their families, and other pest control workers may have contact with a variety of potentially hazardous substances including pesticides, solvents, fuels and oils, engine exhaust, dust and zoonotic viruses and other microbes. All of these exposures have potential health effects that need to be assessed. The multiplicity of these occupational exposures on the farm and the lifestyle of farm families (that is distinctive from the typical urban lifestyles) present both challenges and opportunities for the epidemiological assessment of cancer risk.
Previous epidemiologic studies of farmers, other agricultural workers and pesticide applicators have been limited by inadequate exposure information. In some studies exposures were imputed from characteristics of the farm, the job, or the industry of the study subject. In other studies exposure information was collected from the study subject directly but only after the onset of the disease under investigation, possibly resulting in recall bias. The use of retrospective histories of lifetime exposures in case-control studies has been criticized because of the opportunity for exposure misclassification this could introduce, although in most cases would result in a bias toward the null. In most previous studies, regardless of the study design, the statistical power was limited.
The Agricultural Health Study (AHS) was designed to mitigate previous design limitations by collecting detailed information about occupational and environmental pesticide exposures, lifestyle characteristics and personal and family health history prior to the onset of cancer in a large cohort (n=89,658) of licensed pesticide applicators and their spouses. The spouses of farmer applicators generally live near the fields where pesticide applications occur, and are, therefore, exposed to relatively high environmental (i.e.,"by-stander") exposures. Many spouses also engage in farming activities including pesticide mixing and application. The occupational exposure information on individual pesticides collected in the AHS includes duration of use (years), frequency of use (applications days/year) and intensity of use (e.g., application methods, protective equipment, work practices). The information is updated every five years which will improve the accuracy of the data. The questionnaire data on pesticide exposure are validated with environmental and biological measurements of pesticides and metabolites as well as direct observation of selected cohort members. The study is conducted in two important agricultural states, that are representative of agricultural practices in a large portion of the United States (i.e., mid-west and southeast). Cancer incidence is ascertained by linking to the population based cancers registries in Iowa and North Carolina. Loss to follow-up for determining cancer incidence is minimized by the use of the National Death Index to ascertain vital status, and a variety of address registries which help identify the year a study participant moved out of the state of Iowa and North Carolina and are, therefore, no longer available for cancer incidence follow-up.
This is the first report on the overall cancer incidence among the Agricultural Health Study cohort. Analytical investigations that evaluate individual exposures and cancers are the subject of separate reports.
This work has been funded in part by the U.S. Environmental Protection Agency. It has been subjected to Agency review and approved for publication. Mention of trade names of commercial products does not constitute endorsement of recommendation for use.