Objective Diazinon, a common organophosphate insecticide with genotoxic properties, was previously associated with lung cancer in the Agricultural Health Study (AHS) cohort, but few other epidemiological studies have examined diazinon-associated cancer risk. We used updated diazinon exposure and cancer incidence information to evaluate solid tumour risk in the AHS.

Methods Male pesticide applicators in Iowa and North Carolina reported lifetime diazinon use at enrolment (1993–1997) and follow-up (1998–2005); cancer incidence was assessed through 2010(North Carolina)/2011(Iowa). Among applicators with usage information sufficient to evaluate exposure-response patterns, we used Poisson regression to estimate adjusted rate ratios (RRs) and 95% CI for cancer sites with ≥10 exposed cases for both lifetime (LT) exposure days and intensity-weighted (IW) lifetime exposure days (accounting for factors impacting exposure).

Results We observed elevated lung cancer risks (N=283) among applicators with the greatest number of LT (RR=1.60; 95% CI 1.11 to 2.31; P_trend=0.02) and IW days of diazinon use (RR=1.41; 95% CI 0.98 to 2.04; P_trend=0.08). Kidney cancer (N=94) risks were non-significantly elevated (RR_{LT days}=1.77; 95% CI 0.90 to 3.51; P_trend=0.09; RR_{IW days} 1.37; 95% CI 0.64 to 2.92; P_trend=0.50), as were risks for aggressive prostate cancer (N=656).

Conclusions Our updated evaluation of diazinon provides additional evidence of an association with lung cancer risk. Newly identified links to kidney cancer and associations with aggressive prostate cancer require further evaluation.