Epidemiological response to a suspected excess of cancer among a group of workers exposed to multiple radiological and chemical hazards

OBJECTIVE An excess of cancer was suspected by workers of the metallurgy department at the French Atomic Energy Commissariat (CEA) after several deaths from cancer were reported in 1983 and 1984. After a descriptive study performed by the CEA in 1985 the results of which were not conclusive enough to put an end to the controversy, the present cohort study was undertaken in 1989. METHODS As no specific exposure, or a precise cancer site was suspected, it was decided to include all subjects who had worked at the metallurgy department for at least 1 year between 1950 and 1968. The cohort was followed up to 31 December 1990. Individual occupational exposures were determined retrospectively for each year from 1950 to 1990, both qualitatively (annual job, and hazard records, and assistance from former workers) and quantitatively (for external radiation). On the basis of these exposures, three types of occupational tasks were identified: handling of chemicals, radionuclides, and external radiation. Standardised mortality ratios (SMRs) were calculated to estimate the risk of death, and the existence of an association between risk of cancer and each of the three tasks was tested. RESULTS The cohort included 356 workers, followed up for an average of 30 years (total of 10 820 person-years). The number of deaths from all causes and from all cancer sites were respectively 44 and 21. No excess of cancer deaths was found for the study period (SMR 0.77), nor was there a peak in 1983–4. The risk of death from all cancer sites increased with the duration of exposure to chemicals. CONCLUSION The results do not justify the workers' impression of an excess of cancer. They suggest, however, that the duration of work at some tasks that involved handling chemicals may be an indicator of risk of cancer. Communication to the workers during the study played an important part in reducing their concern, contributing to their better understanding of the results.