The latest findings, which were based on the results of six earlier studies on the herbicide, showed that the chemical significantly raised the risk of non-Hodgkin lymphoma -- the type of cancer affecting Dewayne Johnson, a former school groundskeeper who regularly used Roundup.
"All of the meta-analyses conducted to date, including our own, consistently report the same key finding: exposure to GBHs (glyphosate-based herbicides) are associated with an increased risk of NHL," the authors of the University of Washington report wrote.
Previous research found a link between glyphosate and shorter pregnancies, and thousands of cancer patients have alleged that the weedkiller Roundup was a factor in their cancers.
Last year, a court awarded Dewayne Johnson nearly $300 million, later reduced to $78 million, in a lawsuit against Monsanto. The jury found that the company had failed to warn him and other consumers about the risks of the product.
‘There are some real concerns’
Bayer, the company that purchased Monsanto last year, has maintained that “hundreds of studies indicate glyphosate doesn’t cause cancer.” The latest research appears to contradict that assertion.
"This research provides the most up-to-date analysis of glyphosate and its link with Non-Hodgkin Lymphoma, incorporating a 2018 study of more than 54,000 people who work as licensed pesticide applicators," co-author and doctoral student Rachel Shaffer said in a statement.
The researchers said they focused on people with the “highest exposure” to the herbicide because if Roundup wasn’t carcinogenic, as Bayer claims, even a high degree of exposure shouldn’t raise cancer risk.
“From a population health point of view, there are some real concerns,” said Lianne Sheppard, one of the study’s co-authors.
In a statement, Bayer said the new analysis "provides no scientifically valid evidence that contradicts the conclusions of the extensive body of science demonstrating that glyphosate-based herbicides are not carcinogenic."
The company said the analysis employed the use of "statistical manipulation" and that it contained "serious methodological flaws.”
The new research has been published in Mutation Research.