Methyl Isocyanate and Carcinogenesis: Bridgeable Gaps in Scientific Knowledge

Methyl isocyanate may have a role in cancer etiology, although the link is unclear. There is evidence in theliterature that it can induce cancer in animals but the carcinogenic potency is weak. Pheochromocytoma ofadrenal medulla and acinar cell tumors of pancreas have been observed in methyl isocyanate exposed animals.Conversely, emerging data from population-based epidemiological studies are contradictory since there is noevidence of such cancers in methyl isocyanate exposed humans. Recently, we reported a high prevalence of breastand lung cancers in such a population in Bhopal. In vitro findings appearing in the latest scientific literaturesuggest that genomic instability is caused by methyl isocyanate analogs in lung, colon, kidney, ovary epithelialcells, and that hepatocytes may undergo oncogenic transformation, have obvious implications. The conflictinginformation prompted us to present this update over the last three decades on methyl isocyanate-inducedcancers after an extensive literature search using PubMed. While the pertinent literature remains limited,with a scarcity of strong laboratory analyses and field-epidemiological investigations, our succinct review ofanimal and human epidemiological data including in vitro evidences, should hopefully provide more insight toresearchers, toxicologists, and public health professionals concerned with validation of the carcinogenicity ofmethyl isocyanate in humans.