A study published in 2003 examined pooled data from three case-control studies on NHL in the midwestern United States. The study, by De Roos and colleagues, was an analysis of 47 pesticides simultaneously, controlling for confounding by other pesticides as risk factors for NHL in a pooled analysis of 3417 male farm workers. They noted that the use of particular pesticides, including the insecticides coumaphos, diazinon, fonofos, chlordane, dieldrin, and copper acetoarsenite, as well as the herbicides atrazine, glyphosate, and sodium chlorate, were associated with increased NHL risk, with a trend toward increasing risk with exposures to multiple pesticides. The OR for glyphosate increasing the risk of developing NHL was 2.1 with a 95% confidence interval (CI) of 1.1 to 4.0 (OR 2.1; 95% CI: 1.1-4.0). This doubling of the risk was statistically significant. The significant risk remained after logistic regression was performed. A subsequent hierarchical regression analysis reduced the OR to 1.6 (95% CI: 0.9-2.8).
In 2002, Hardell and colleagues reported a pooled analysis performed on two case-control studies from Sweden, one on NHL and another on hairy cell leukemia. The analysis included 515 cases and 1141 controls and specifically queried multiple different pesticides. Among the herbicides, there was a significant association between NHL risk and glyphosate exposure (OR 3.04; 95% CI: 1.08-8.52). A subsequent population-based case-control study published in 2008 from the same group of researchers assessed exposure to pesticides as a risk factor for NHL. This study included a total of 910 cases and 1016 controls enrolled from 12/01/1999 to 04/30/2002. Both arms had a greater than 90% participation rate in the survey. This study showed that exposure to glyphosate imparted a twofold risk of NHL (OR 2.02; 95% CI: 1.10-3.71) and a stronger association with CLL/SLL (OR 3.35; 95% CI: 1.42–7.89. The association with NHL was strengthened with >10 years latency period (OR 2.26; 95% CI: 1.16-4.40) meaning the association was stronger in those patients with exposure greater than 10 years in the past as opposed to only more recent exposure. This comports with the known delay in manifestation of lymphomas due to the necessary development of multiple different mutations over time. The association with NHL was also stronger in those patients who used glyphosate more than 10 lifetime days v. patients who used it less than 10 lifetime days (OR 2.36; 95% CI: 1.04-5.37.)