A Prospective Study of Cancer and Other Diseases Among Men and Women in Agriculture

Trial Information

A Prospective Study of Cancer and Other Diseases Among Men and Women in Agriculture

The "Agricultural Health Study" (AHS) is a collaborative effort between the National Cancer
Institute and the National Institute of Environmental Health Sciences. The US Environmental
Protection Agency and the National Institute for Occupational Safety and Health are
providing support for a limited exposure assessment effort.

Initial data collection on a prospective cohort of 89,656 study subjects has been completed
as of December 1997 (Phase I). Participants completed questionnaires that included items on
pesticides used, other agricultural exposures, and work practices that modify exposure as
well as on other activities that may affect either exposure or disease risks (e.g., diet,
exercise, alcohol consumption, medical conditions, family history of cancer, other
occupations and smoking history). Phase II of the study (1998-2003) updated information on
occupational exposures, diet, work practices and medical history by means of a computer
assisted telephone interview. We also collected buccal cells on a sample of 35,164 study
participants to assess the effect of inheritable polymorphisms and the interaction of
environment and genomic predisposition.

The stimulus for this prospective investigation comes from the growing evidence that,
despite a low mortality overall, farmers experience an excess of several cancers. These
excesses have been observed in retrospective epidemiological studies among agricultural
workers in several countries. Excess cancers are observed for the lymphatic and
hematopoietic system, connective tissue, skin, brain, prostate, stomach and lips. Several
of these tumors (e.g., brain, NHL, multiple myeloma, and prostate) are also increasing in
the general population in many of these countries. This suggests a common set of exposures
may explain the high rates in farmers and 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. Our cohort study includes all
registered pesticide applicators in Iowa and North Carolina and the spouse of applicators
who are farmers. The health effects of pesticide use are the primary focus of the study.
The influence of other farm exposures is also being evaluated.

Phase III data collection activity was completed in February 2010. The focus of the phase
III follow-up period (2004- 2010) was to update exposure information and health histories by
means of a computer assisted interview, to follow the cohort to determine disease incidence
and mortality, and to collect buccal cell samples from newly-developing cancer cases (and
matched controls) who have not previously donated a sample. Phase III follow-up interviews
were completed with 44,130 participants; specifically, interviews were completed with 24,171
applicators and 19,959 spouses. Additionally, 1,245 buccal samples were collected in Phase
III from among selected participants with incident cancers. No adverse events were reported
during Phase III.

The cohort continues to be followed through the cancer registries within Iowa and North
Carolina, the Social Security Administration database, state vital statistics offices,
National Death Index, and various in-state databases, such as the listing of registered
pesticide applicators. Individuals who enrolled into the study but who are no longer at the
address given during enrollment (based on subsequent attempts at followup) have been
submitted and will continue to be submitted (through NIOSH) in the standard format to the
IRS under their Project 057 Taxpayer Address Request Program. Identifying data provided to
the IRS include only SSN and the first four letters of the last name of the cohort member.
IRS provides in return the most current address in IRS records if a match (SSN + all four
letters of last name) is found. The purpose of this effort is to identify members of the
cohort who have moved out of state, to enable adjustment of person-years for incidence and
mortality calculations. Persons who have moved out of state can be followed for vital
status and cause of death, but not for cancer incidence.

Additionally, the Iowa field station maintains a database of AHS cohort children in Iowa
established through linkage of the cohort to Iowa birth certificates. This composite of
children identified from the Iowa cohort data and birth certificates through 2008 (over
35,000 live births), is linked to Iowa drivers' license tapes, the Iowa cancer incidence
database, the Iowa mortality database, the NDI, and the Internal Revenue Service (to obtain
updated addresses). As with the adult linkages, these data are held by the AHS coordinating
center and are available for secondary analysis.

Continuation of the protocol will provide a valuable epidemiologic resource to help prevent
cancers in the future by identifying risk factors in the rural/agricultural environment.
Because more cases of important cancer outcomes occur in this cohort every year, potential
cancer causes can be evaluated with increased statistical power. Larger numbers of cases
also allow for statistical control of confounding factors and more meaningful conclusions
about cancer risk, and, for some relatively infrequent cancers, such as the lyphomas and
leukemias, greater follow-up time is necessary to make any meaninful observations.

The process of planning for Phase IV has begun and it is expected to begin before the close
of FY2011.