Cancer patterns of lung, oropharynx and oral cavity cancer in relation to gas exposure at Bhopal

Background: In Bhopal, India, on 2 December 1984, a chemical disaster caused by a gas leak mostly of methyl isocyanate (MIC) from the Union Carbide Factory led to massive mortality and morbidity of the population. This is the first study to shed light on the cancer experience of the Bhopal population as a result of exposure to a mixture of gases which have highly toxic and potentially carcinogenic properties. To observe the effect of gas exposure, incidence rates of the three most common cancer sites (lung, oropharynx and oral cavity) from 1987 to 1992 among the municipal wards were studied in males. Methods: Relative risks (RR) using cases from the cancer registry and controls from a tobacco survey were estimated for the gas-affected regions. Results: Based on a descriptive study the relative risks of 1.4, 1.3 and 0.7 for lung, oropharynx and oral cavity cancer, respectively, for gas-affected regions in the year 1992 in comparison to gas-unaffected regions and the year 1987-1990 combined were estimated. In the case-control study the RRs of 0.9, 1.4 and 1.2 for lung, oropharynx (adjusted for smoking) and oral cavity cancer, respectively, (adjusted for tobacco chewing) were estimated as the effect of the gas accident. Conclusion: The full potential of excess risk, if any, may not manifest for 15-20 years after the accident.