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

Pahwa M Harris SA, Hohenadel K, McLaughlin JR, Spinelli JJ, Pahwa P, Dosman JA, Blair A. Pesticide use, immunologic conditions, and risk of non-Hodgkin lymphoma in Canadian men in six provinces. International Journal of Cancer 2012; 131(11):2650-2659.

Abstract

Pesticide exposures and immune suppression have been independently associated with the risk of non-Hodgkin lymphoma (NHL), but their joint effect has not been well explored. Data from a case–control study of men from six Canadian provinces were used to evaluate the potential effect modification of asthma, allergies, or asthma and allergies and hay fever combined on NHL risk from use of: (i) any pesticide; (ii) any organochlorine insecticide; (iii) any organophosphate insecticide; (iv) any phenoxy herbicide; (v) selected individual pesticides [1,1?-(2,2,2-trichloroethylidene)bis[4-chlorobenzene]; 1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane (DDT), malathion, (4-chloro-2-methylphenoxy)acetic acid (MCPA), mecoprop, and (2,4-dichlorophenoxy)acetic acid (2,4-D); and (vi) from the number of potentially carcinogenic pesticides. Incident NHL cases (n = 513) diagnosed between 1991 and 1994 were recruited from provincial cancer registries and hospitalization records and compared to 1,506 controls. A stratified analysis was conducted to calculate odds ratios (ORs) adjusted for age, province, proxy respondent, and diesel oil exposure. Subjects with asthma, allergies, or hay fever had non-significantly elevated risks of NHL associated with use of MCPA (OR = 2.67, 95% confidence interval [CI]: 0.90–7.93) compared to subjects without any of these conditions (OR = 0.81, 95% CI: 0.39–1.70). Conversely, those with asthma, allergies, or hay fever who reported use of malathion had lower risks of NHL (OR = 1.25, 95% CI: 0.69–2.26) versus subjects with none of these conditions (OR = 2.44, 95% CI: 1.65–3.61). Similar effects were observed for asthma and allergies evaluated individually. Although there were some leads regarding effect modification by these immunologic conditions on the association between pesticide use and NHL, small numbers, measurement error and possible recall bias limit interpretation of these results.

What is non-Hodgkin lymphoma?

Non-Hodgkin lymphoma (NHL) is a term used to describe a group of blood cancers that start growing in white blood cells, which are part of the body’s immune system. NHL occurs in the lymph nodes, spleen, thymus and bone marrow. The causes are unclear, but NHL has been linked to autoimmune diseases, a weakened immune system, nuclear radiation and exposure to certain chemicals including pesticides.The incidence of  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, yet the causes of this disease are not well known.

How do immune conditions and pesticide exposure affect the risk of NHL?

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 goal 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 various pesticide groups, selected individual pesticides, 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. The study, which was published in the International Journal of Cancer, improves upon the few previous analyses of these relationships by focusing on commonly used pesticides and it has wide applicability in Canada.