An Investigation Of Organochlorine Insecticide Use And The Risks Of Non-Hodgkin Lymphoma: Findings From The North American Pooled Project

Linda KACHURI, Cancer Care Ontario; Dalla Lana School of Public Health at the University of Toronto, Canada
HARRIS S. 1,2,3 , SPINELLI J. 4 , BLAIR A. 5 , PAHWA M. 1,2 , HOAR ZAHM S. 5 , CANTOR K. 5 , WEISENBURGER D. 6 , PAHWA P. 7,8 , DOSMAN J. 8 , MCLAUGHLIN J. 2,3,9,10 , DEMERS P. 2,3 , BEANE FREEMAN L. 5

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

Purpose: Organochlorine insecticides are persistent, bio-accumulative compounds that are frequently used worldwide. Recently, the International Agency for Research on Cancer (IARC) classified several organochlorines as Group 1 and Group 2A carcinogens for non-Hodgkin lymphoma (NHL). However, some studies were limited by low statistical power and did not assess exposure-response relationships. In this analysis, we investigated self-reported organochlorine exposure with respect to NHL risk in a large population-based study: the North American Pooled Project (NAPP).  

Methods: Four case-control studies conducted in Canada (1991-1994) and Midwestern U.S. (1981-1986) were pooled to form the NAPP, which includes 1690 NHL cases and 5131 controls. Logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI) for organochlorine use (ever/never exposed) and duration of use (years), with adjustment for demographic characteristics and NHL risk factors. 

Results: Compared to unexposed subjects, statistically significant associations with NHL risk were observed among those reporting use of chlordane (OR=1.44, 95% CI=1.13-1.84), DDT (OR=1.32, 95% CI=1.10-1.58), dieldrin (OR=1.52, 95% CI=1.04-2.22), heptachlor (OR=1.47, 95% CI=1.02-2.11) and lindane (OR=1.69, 95% CI=1.31-2.17). A consistent exposure-response trend was observed for years of lindane use: OR>0 to 5=1.36, OR5 to >10=1.87, OR10 to >15=1.93, OR>15=2.01 (p-trend=<.0001). Increased risk of NHL was observed for >15 years of DDT use (OR=1.52, 95% CI=1.06-2.17, p-trend=0.001) Non-monotonic but positive trends in NHL risk with increasing exposure duration were also observed for chlordane (p-trend=0.03) and heptachlor (p-trend=0.04).

Conclusions: This analysis uncovered several statistically significant associations for organochlorine use and NHL risk. The increased sample size of the NAPP allowed us to estimate risk across more refined exposure levels and identify significant exposure-response trends for lindane. Overall, these findings contribute to the epidemiologic literature supporting the recent IARC classification.

Funding Source: Canadian Cancer Society Research Institute (#703055); U.S. National Institutes of Health Intramural Research Program, National Cancer Institute