The International Agency for Research on Cancer (IARC) - part of the World Health Organisation - has downgraded its former classification of the phthalate DEHP as a potential human carcinogen. In January 2000, an IARC working group decided in the light of a large body of other relevant data, including evidence from genetically engineered mice, that the chemical should instead be described as " not classifiable as to carcinogenicity to humans". DEHP was initially classified as a potential carcinogen following rodent studies, in which it was found to cause liver tumours through a mechanism called peroxisome proliferation when administered at high doses. IARC has now ruled that the mechanism by which DEHP increases the incidence of liver tumours in rats and mice is not relevant to humans.