A large long-term study on the use of the big-selling weedkiller glyphosate by agricultural workers in the United States has found no firm link between exposure to the pesticide and cancer, scientists said on Thursday.
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Published in the Journal of the National Cancer Institute (JNCI), the study found there was "no association between glyphosate", the main ingredient in Monsanto's popular herbicide RoundUp, "and any solid tumors or lymphoid malignancies overall, including non-Hogkin Lymphoma (NHL) and its subtypes."
It said there was "some evidence of increased risk of acute myeloid leukemia (AML) among the highest exposed group", but added "this association was not statistically significant" and would require more research to be confirmed.
The findings are likely to impact legal proceedings taking place in the United States against Monsanto, in which more than 180 plaintiffs are claiming exposure to RoundUp gave them cancer - allegations that Monsanto denies.
The findings may also influence a crucial decision due in Europe this week on whether glyphosate should be re-licensed for sale across the European Union.
That EU decision has been delayed for several years after the World Health Organization's International Agency for Research on Cancer (IARC) reviewed glyphosate in 2015 and concluded it was "probably carcinogenic" to humans. Other bodies, such as the European Food Safety Authority, have concluded glyphosate is safe to use.
The research is part of a large and important project known as the Agricultural Health Study (AHS), which has been tracking the health of tens of thousands of agricultural workers, farmers and their families in Iowa and North Carolina.
Since the early 1990s, it has gathered and analyzed detailed information on the health of participants and their families, and their use of pesticides, including glyphosate.
Reuters reported in June how an influential scientist was aware of new AHS data while he was chairing a panel of experts reviewing evidence on glyphosate for the International Agency for Research on Cancer (IARC) in early 2015.
But since it had not at that time been published, he did not tell the experts panel about it and IARC's review did not take it into account.
The publishing of the study on Thursday comes more than four years since drafts based on the AHS data on glyphosate and other pesticides were circulating in February and March 2013.
In a summary conclusion of the results, the researchers, led by Laura Beane Freeman, the principal investigator of the AHS at the U.S. National Cancer Institute, reported that among 54,251 (pesticide) applicators in the study, 44,932, or 82.9 percent of them used glyphosate.
"Glyphosate was not statistically significantly associated with cancer at any site," the conclusion said.
The researchers said they believed the study was the first to report a possible association between glyphosate and AML, but that it could be the result of chance and should be treated with caution.
(Reporting by Kate Kelland, Editing by William Maclean)