An American study has shown that exposure to certain pesticides doubles a person's risk of developing an abnormal blood condition called monoclonal gammopathy of undetermined significance (MGUS)-a condition that can lead to a painful cancer of the plasma cells in the bone marrow, called myeloma.
The study involved 678 individuals who apply pesticides, culled from a U.S. Agricultural Health Study of over 50,000 farmers.
"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 Dr. Ola Landgren, 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," Dr. Landgren said.
Senior study author and NCI investigator Michael Alavanja added: "As several million Americans use pesticides, it's important that the risks of developing MGUS from the use of pesticides is known."
The blood of the participants, aged 30-94, was assessed for MGUS prevalence. They 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.
Individuals with prior histories of lymphoproliferative malignancies, such as multiple myeloma or lymphoma, were excluded.
The researchers monitored cancer incidence and mortality annually, and, after five years, conducted follow-up interviews to update the information about participants' occupational exposures, medical histories, and lifestyle factors.
The team compared the results from the pesticide-exposed group with the assessments of 9,469 men from the general population of Olmsted County, Minnesota.
In the pesticide-exposed group, no MGUS cases were observed among those who were less than 50 years of age, but the prevalence of the disorder in those older than 50 was 6.8 percent, which was 1.9 times higher than the general population study group of men in Minnesota.
The researchers also evaluated the potential association between MGUS prevalence and 50 specific pesticides for which usage data were known, and observed a significantly increased risk among users of dieldrin (an insecticide), carbon-tetrachloride/carbon disulfide (a fumigant mixture), and chlorothalonil (a fungicide).
Several other insecticides, herbicides, and fungicides were also associated with MGUS, but not significantly.
"Our findings are intriguing. If replicated in a larger sample from our study and other large studies, further work should focus on gaining a better understanding of the molecular basis of MGUS and multiple myeloma. Ultimately, this will result in the identification of novel molecular targets involved in the progression from MGUS to multiple myeloma and in the development of targeted therapies," said Dr. Landgren.
The study will appear in the June 18 issue of the journal Blood.