Dutch regulator: Italian study claiming glyphosate causes cancer is unreliable

Experts at the Dutch Board for the Authorisation of Plant Protection Products and Biocides (Ctgb) say a recent Italian study linking glyphosate, an ingredient in weedkillers like Roundup, to cancer in lab animals is flawed and does not change their assessment of the substance.

According to the Ctgb, the scientific publication released earlier this month “does not lead to the conclusion that the substance glyphosate is carcinogenic.” The agency reviewed the study at the request of the Ministry of Agriculture and rejected the authors’ claim that their rat experiments provided “robust evidence” of carcinogenicity.

The Ctgb said the reliability of the research is difficult to verify because the raw data were not made available. For that reason, the agency recommended that European Union authorities responsible for pesticide and food safety request and review the complete underlying data.

The Ctgb also raised several substantive objections to how the study was conducted and presented. One major criticism was that the researchers combined different types of tumors that developed in the rats, even though those tumors originate through unrelated biological processes. “This results in higher statistical significance, but it is not biologically correct,” the agency concluded.

Another issue concerns the rats themselves. The Sprague-Dawley strain used in the experiments is known to frequently develop spontaneous tumors. “It cannot currently be said that the tumors found are a consequence of exposure to glyphosate or glyphosate-containing products,” the Ctgb said. Some tumor types appeared in only a single animal, and in other studies where rats were given higher doses of glyphosate, such tumors were not observed at all.

The agency also noted inconsistencies in the results. In some cases, a rat exposed to a low dose of glyphosate developed a tumor, while rats exposed to higher doses did not. “If glyphosate were causing tumors, it would be expected that higher dosages would lead to more or faster tumor formation,” the Dutch evaluators wrote. “Such a dose-response relationship is not seen in this study.”