Lifetime Pesticide Use and Monoclonal Gammopathy of Undetermined Significance in a Prospective Cohort of Male Farmers.

BACKGROUND: Farmers have a higher incidence of multiple myeloma, and there is suggestive evidence of an elevated prevalence of its precursor, monoclonal gammopathy of undetermined significance (MGUS), relative to the general population. Pesticide exposures are suspected to play a role; however, the biologic plausibility for associations with multiple myeloma remains unclear.

OBJECTIVES: Our objectives were to examine the prevalence of MGUS and evaluate associations with a wide range of pesticides in a large sample of farmers.

METHODS: We obtained sera and assessed MGUS among 1,638 male farmers ≥50 years of age in the Agricultural Health Study (AHS), a prospective cohort in Iowa and North Carolina. Odds ratios (ORs) and 95% confidence intervals (CIs) were computed to estimate associations with MGUS for recent use (within the 12 months before phlebotomy) and cumulative intensity-weighted lifetime days of use of specific pesticides.

RESULTS: The age-standardized MGUS prevalence was significantly elevated among AHS farmers (7.7%) compared with demographically similar men in the National Health and Nutrition Examination Survey (2.8%) or Olmsted County, Minnesota (3.8%; p<0.001). Recent use of permethrin was associated with MGUS [recent use vs. no recent use, OR=1.82 (95% CI: 1.06, 3.13)], especially among those who had also used it in the past [recent and past use vs. never use, OR=2.49 (95% CI: 1.32, 4.69)]. High intensity-weighted lifetime use of the organochlorine insecticides aldrin and dieldrin was associated with MGUS relative to those who never used either of these pesticides [OR=2.42 (95% CI: 1.29, 4.54); ptrend=0.006]. We also observed a positive association with high lifetime use of petroleum oil/distillates as an herbicide, as well as an inverse association with fonofos use.

DISCUSSION: This is the largest investigation of MGUS in farmers and the first to identify an association with MGUS for permethrin, a pyrethroid insecticide previously associated with multiple myeloma. Given the continued widespread use of permethrin in various residential and commercial settings, our findings may have important implications for exposed individuals in the general population. https://doi.org/10.1289/EHP6960.