Glyphosate exposure did not increase the risk of UVR-induced skin tumors in hairless mice.

Glyphosate (GLY) is the most widely used pesticide in the world. Agricultural workers are exposed to GLY via ingestion and skin contact. GLY may generate epigenetic changes that might be carcinogenic. However, whether GLY is carcinogenic remains controversial. We investigated whether GLY was co-carcinogenic with ultraviolet radiation (UVR) by monitoring skin tumor development in hairless mice. Four groups of immunocompetent mice (total, N = 96) were used in the study. Two groups received GLY in drinking water (5 µg/mL or 50 µg/mL), one group received 50 µL topical GLY (6.59% w/w) three times per week, and a UVR control group received only tap water. All groups were given UVR until they developed three 4-mm tumors or one 12-mm tumor. Times to development of first, second, and third skin tumors were recorded. In both groups given GLY orally (medians, 163 days) and the group given GLY topically (median, 170 days), the times to skin tumor development were not significantly different from the control group (median, 163 days; p ≥ 0.535). Mass spectrometry imaging showed that topically applied GLY was present on the surface of the skin but not detectable within the skin. There were no differences in weight, erythema, or pigmentation. When combined with UVR, GLY in drinking water or directly applied to skin was not associated with increased skin tumor development.