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

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 5 513) 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 5 2.67, 95% confidence interval [CI]: 0.90-7.93) compared to subjects without any of these conditions (OR 5 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 5 1.25, 95% CI: 0.69-2.26) versus subjects with none of these conditions (OR 5 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.The incidence of non-Hodgkin lymphoma (NHL) showed a steady worldwide increase from 1950, but plateaued in the late 1990s.1 In 2011, NHL was the fifth most frequently occurring cancer and the sixth leading cause of all cancer deaths in Canada.2 The causes of NHL are not well-known. 1,3Immune suppression is the most clearly established risk factor for NHL 3-6 because of substantially elevated risks among individuals with autoimmune disease, primary or acquired immunodeficiencies, and organ transplant recipients.1,3 Risk appears to increase with the degree of immune deficiency.7 Factors that suppress the immune system, like chemical exposures, may facilitate the development of NHL. A number of occupational and environmental factors have been associated with NHL. 5,8 Farming has been linked to NHL 9 overall and for major NHL subtypes. 1 This observation has prompted research on agricultural chemicals, such as pesticides, solvents, fuels, oils, and other agents that are potentially carcinogenic. [10][11][12] Use of some specific pesticides may contribute to the increased incidence of NHL.13-15 For example, occupationa...

Non-Hodgkin Lymphoma and Occupational Exposure to Agricultural Pesticide Chemical Groups and Active Ingredients: A Systematic Review and Meta-Analysis

“…Two papers reported results from the Cross-Canada Study of Pesticides and Health, which was a case control study conducted in six Canadian provinces [43,47]. Population based controls were frequency matched to NHL cases, diagnosed 1991–1994, based on age and province of residence.…”

“…The questionnaires used for this study were based on the one used in the USA National Cancer Institute led case-control studies [20,23,30,56,59,60] in Nebraska [18,58] and Kansas [34]. McDuffie et al [43] and Pahwa et al [47] present results from some of the same analyses with the same population. When the same analysis was reported in both papers we selected the effect estimate from the paper by Pahwa et al [47] because the authors excluded four NHL cases based on pathology review that occurred subsequent to the analyses reported in McDuffie et al [43].…”

Increased cancer burden among pesticide applicators and others due to pesticide exposure

“…128 In yet another article from the 6 Canadian provinces study, the joint effect of pesticide exposure and immune suppression was preliminarily evaluated. 61 Study participants with asthma or hay fever had nonsignificantly elevated risks of NHL associated with the use of MCPA (OR, 2.67; 95% CI, 0.90-7.93) compared with participants without any of these conditions (OR, 0.81; 95% CI, 0.39-1.70).…”

Organophosphate insecticide use and cancer incidence among spouses of pesticide applicators in the Agricultural Health Study

“…A recent AHS analysis of male applicators found null associations with malathion use and NHL risk overall 18. Additionally, some case–control studies have shown a positive association for malathion use and NHL 9 46 47. Adjustment for other variables shown to be associated with NHL risk in farming populations, including whether or not our study participants grew up on a farm, their self-reported history of physician diagnosed allergies and contact with farm animals, did not alter the relationships in our study.…”