Exposure to certain pesticides doubles the risk of developing an abnormal blood condition called MGUS (monoclonal gammopathy of undetermined significance) compared with individuals in the general population, according to a study involving 678 individuals who apply pesticides. The data was culled from a U.S. Agricultural Health Study of over 50,000 farmers.

The disorder, characterized by an abnormal level of a plasma protein, requires lifelong monitoring as it is a pre-cancerous condition that can lead to multiple myeloma, a painful cancer of the plasma cells in the bone marrow. The study will appear in the June 18 issue of Blood, the official journal of the American Society of Hematology.

"Previously, inconclusive evidence has linked agricultural work to an increased multiple myeloma risk. Our study is the first to show an association between pesticide exposure and an excess prevalence of MGUS," said lead author Ola Landgren, MD, PhD, of the National Cancer Institute (NCI), which is part of the National Institutes of Health, U.S. Department of Health and Human Services. "This finding is particularly important given that we recently found in a large prospective cancer screening study that virtually all multiple myeloma patients experienced a MGUS state prior to developing myeloma."

"As several million Americans use pesticides, it's important that the risks of developing MGUS from the use of pesticides is known," added senior study author and NCI investigator Michael Alavanja, DrPH.

The blood of study participants, who were individuals licensed to apply restricted-use pesticides, was assessed for MGUS prevalence. The median age of participants was 60 years (range 30-94 years), and all lived in either Iowa or North Carolina. Participants also completed questionnaires providing comprehensive occupational exposure information for a wide range of pesticides, including information such as the average number of days of pesticide use per year, years of use, use of protective gear while applying pesticides, and pesticide application methods. Information on smoking and alcohol use, cancer histories of the participants' first-degree relatives, and other basic demographic and health data were also obtained. Individuals with prior histories of lymphoproliferative malignancies (such as multiple myeloma or lymphoma) were excluded. Cancer incidence and mortality were monitored annually, and, after five years, follow-up interviews were conducted to update the information about participants' occupational exposures, medical histories, and lifestyle factors.