Glyphosate is a widely used herbicide worldwide. In 2015, the International Agency for Research on Cancer (IARC) reviewed glyphosate cancer bioassays and human studies, declared that the evidence for carcinogenicity of glyphosate is sufficient in experimental animals.  We analyzed ten glyphosate rodent bioassays, including those in which IARC found evidence of carcinogenicity, using a meta-analytic procedure that adjusts for the large number of tumors eligible for statistical testing and provides valid false-positive probabilities.  The test statistics for these global tests are functions of p-values from a standard test for dose-response trends applied to each specific type of tumor.  We evaluated three global tests, using as test statistics the smallest p-value from a standard statistical test for dose-response trend and the number of such tests for which the p-value is less than or equal to 0.05 or 0.01.  The false-positive probabilities obtained from two implementations of these three global tests are: smallest p-value: 0.26, 0.17, p-values ≤ 0.05: 0.08, 0.12, p-values ≤ 0.01: 0.06, 0.08.  In addition, we found more evidence for negative dose-response trends than positive.  Thus, we found no strong evidence that glyphosate is an animal carcinogen.  The main cause for the discrepancy between IARC’s finding and ours appears to be that IARC did not account for the large number of statistical tests performed in the bioassays they reviewed and the resulting multiple comparison problem.  This work provides a more comprehensive analysis of the animal carcinogenicity data for this important herbicide than previously available.

Individual animal data from rodent carcinogenicity bioassays for glyphosate. We extracted individual animal data from ten glyphosate rodent carcinogenicity bioassays.

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