Evaluation of the carcinogenicity of chemicals: a review of the Monograph Program of the International Agency for Research on Cancer (1971 to 1977).

In 1971 the International Agency for Research on Cancer initiated a program on the evaluation of the carcinogenic risk of chemicals to humans, which concentrated on the production of monographs on individual chemicals. A review of this ongoing program is presented here as a contribution to the discussion of primary prevention of cancer. A total of 368 chemicals were evaluated in the first 16 volumes of the International Agency for Research on Cancer monographs. For 26 chemicals (or industrial processes), a positive association between exposure and the occurrence of cancer in humans was observed. For 221 chemicals, some evidence of carcinogenicity was found in at least one species of experimental animals. However, no evaluation of the carcinogenic risk of these chemicals to humans was made, either because no epidemiological studies or case reports were available or because the results of available human studies were inconclusive. For the remaining 121 chemicals, the available data were inadequate for an evaluation of the presence or absence of a carcinogenic effect in experimental animals or humans. The criteria on which the carcinogenicity of chemicals to humans and/or experimental animals was assessed, from the initiation of this program in 1971 until 1977, have recently been revised and are briefly discussed.