Pesticide use, immunologic conditions, and risk of non-Hodgkin lymphoma in Canadian men in six provinces

Research Summary

Manisha Pahwa, Shelley A Harris, Karin Hohenadel, John R McLaughlin, John J Spinelli, Punam Pahwa, James A Dosman, Aaron Blair. 

The incidence of non-Hodgkin lymphoma (NHL) has steadily increased worldwide since 1950. In 2011, NHL was the fifth most frequently occurring cancer and the sixth leading cause of all cancer deaths in Canada. The causes of this disease are not well known.

Exposure to pesticides and a suppressed immune system have been independently associated with the risk of NHL. Previous studies of the joint effect of these two risk factors have found that the odds of NHL from pesticide exposure may be elevated among asthmatics compared to non-asthmatics. However, these findings are not consistent and require further exploration.

The objective of this project was to determine if the relationship between pesticide use and risk of NHL differed in men who had immune conditions compared to those who did not. We used data from the Cross-Canada Study of Pesticides and Health, a case-control study of Canadian men aged 19 years and older in six provinces, to analyze the effects of asthma, allergies, or asthma and allergies and hay fever on NHL risk from the use of pesticide groups (organochlorine insecticides, organophosphate insecticides, and phenoxy herbicides), selected individual pesticides (DDT, malathion, MCPA, mecoprop, and 2,4-D), and from the number of potentially carcinogenic pesticides. We did separate analyses for men with and without these immune conditions to calculate odds ratios that were adjusted for age, province, proxy respondent, and diesel oil exposure.

Although there were some interesting leads that these immune conditions may affect the association between pesticide use and NHL, the interpretation of our results are limited by small numbers and possible recall bias. The odds of NHL were elevated from the use of DDT and MCPA in men with asthma, allergies or asthma and allergies and hay fever compared to men without any of these immune conditions.  On the other hand, the risks of NHL associated with the use of organophosphate insecticides, malathion, and mecoprop were higher among individuals without asthma, allergies, or asthma and allergies and hay fever versus those with any of these immune conditions. These could represent new leads or may simply be chance findings.

Our study improves upon the few previous analyses of these relationships by focusing on commonly used pesticides and it has wide applicability in Canada. Nevertheless, further research is needed with larger numbers or pooled studies and with better characterization of pesticide exposures and immune conditions.