FARMING AND PROSTATE-CANCER MORTALITY

Although farmers appear to be at an increased risk of prostate cancer, the specific exposures which produce the excess risk remain unexplain ed. This study was based on a retrospectively assembled cohort of male Manitoba, Saskatchewan, and Alberta, Canada, farmers age 45 years or older identified in the 1971 Canadian censuses of population and agric ulture. The cohort was linked to the Canadian National Mortality Datab ase using an iterative computer record linkage system for the period J une 1971 to the end of 1987. A total of 1,148 prostate cancer deaths a nd 2.213,478 person-years were observed. Using Poisson regression, the study examined the relation between the risk of dying from prostate c ancer and various farm practices as identified on the 1971 Census of A griculture, including exposure to chickens, cattle, pesticides, and fu els. A weak, but statistically significant, association was found betw een number of acres sprayed with herbicides in 1970 and risk of prosta te cancer mortality. When the analysis was restricted to farmers belie ved to be subject to the least amount of misclassification, the risk a ssociated with acres sprayed with herbicides increased (rate ratio (RR ) = 2.23 for 250 or more acres sprayed; 95% confidence interval (Cl) 1 .30-3.84; test for trend, p < 0.01). No other farm exposure examined w as associated with any detectable pattern of increased or decreased ri sk. These findings encourage further research to examine the effects o f herbicides on prostate cancer.