Letter to Dr. Gro Harlem Brundtland, Director-General, WHO

Problems in evaluation of carcinogenicity of chemicals have been recently identified at a WHO organization, the International Agency for Research on Cancer (IARC) in Lyon. Dr. Lorenzo Tomatis, former Director of IARC, suggests that IARC has begun a new trend towards downgrading carcinogen classifications of chemicals on which there were positive results in experimental bioassays (1): \u201cEvidence for carcinogenicity provided by the results of experimental bioassays has been disregarded on the basis of unproven mechanistic hypotheses.\u201d Dr. Tomatis warns that if those hypotheses are shown to be incorrect once they have been tested, very serious consequences for public health may follow. Newly released data on cancer in workers at a U.S. plant making one of the chemicals whose carcinogenic rating was downgraded by IARC, the herbicide atrazine, suggests that positive experimental cancer findings were indeed predictive of carcinogenicity in human