A detailed assessment of glyphosate use and the risks of non-Hodgkin lymphoma overall and by major histological sub-types: findings from the North American Pooled Project

Manisha PAHWA, Cancer Care Ontario, Canada
BEANE FREEMAN L. 2 , SPINELLI J. 3,4 , BLAIR A. 2 , HOAR ZAHM S. 2 , CANTOR K. 2 , PAHWA P. 5,6 , DOSMAN J. 5 , MCLAUGHLIN J. 1,7,8 , WEISENBURGER D. 9 , DEMERS P. 1,7 , HARRIS S. 1,7,10

1 Occupational Cancer Research Centre, Cancer Care Ontario, Toronto, Canada
2 Division of Cancer Epidemiology and Genetics, U.S. National Cancer Institute, Bethesda, U.S.A.
3 British Columbia Cancer Agency Research Centre, Vancouver, Canada
4 School of Population and Public Health, University of British Columbia, Vancouver, Canada
5 Canadian Centre for Health and Safety in Agriculture, University of Saskatchewan, Saskatoon, Canada
6 Department of Community Health and Epidemiology, University of Saskatchewan, Saskatoon, Canada
7 Dalla Lana School of Public Health, University of Toronto, Toronto, Canada
8 Public Health Ontario, Toronto, Canada
9 Department of Pathology, City of Hope Medical Center, Duarte, U.S.A
10 Prevention and Cancer Control, Cancer Care Ontario, Toronto, Canada

Purpose: Glyphosate is the most frequently used herbicide worldwide. The International Agency for Research on Cancer recently classified glyphosate as a probable carcinogen for non-Hodgkin lymphoma (NHL), but the epidemiological studies considered were limited by small sample sizes and a lack of exposure-response data for NHL sub-types. We evaluated potential associations between glyphosate use and NHL risk using detailed information from the North American Pooled Project (NAPP).

Methods: Data from NHL cases (N=1690) and population-based controls (N=5131), recruited from Canada and the Midwest U.S. during the 1980s-1990s for 4 different studies, were recently pooled for the NAPP. Self-reported glyphosate use information was used to assess possible associations with NHL overall and by histological sub-type (follicular lymphoma [FL], diffuse large B-cell lymphoma [DLBCL], small lymphocytic lymphoma [SLL], and other). Odds ratios (OR) and 95% confidence intervals (CI) were estimated with multiple logistic regression models adjusted for demographic and NHL risk factors.

Results: Unadjusted for other pesticides, subjects who ever used glyphosate (N=133) had a significantly elevated NHL risk (OR=1.43, 95% CI: 1.11, 1.83). Glyphosate use for >3.5 years increased SLL risk (OR=1.98, 95% CI: 0.89, 4.39). Handling glyphosate for >2 days/year was associated with significantly higher odds of NHL (OR=2.42, 95% CI: 1.48, 3.96) and DLBCL (OR=2.83, 95% CI: 1.48, 5.41). There were suggestive risk increases (p-value ≤0.02) for NHL, FL, and SLL with greater years*days/year of glyphosate use. Except for SLL, risks attenuated when adjusted for other pesticides.

Conclusions: This analysis suggested that glyphosate use was associated with increased NHL risk. Risk differences by histological sub-type were not consistent across glyphosate use metrics and may have been chance findings. Nevertheless, the NAPP’s large sample size yielded more precise results than previously possible.

Funding source: Canadian Cancer Society Research Institute; U.S. National Institutes of Health Intramural Research Program, National Cancer Institute.