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BACKGROUND: Formaldehyde is mutagenic and, when inhaled at high concentrations, carcinogenic in rats. Some epidemiologic studies have linked occupational exposure to formaldehyde with cancers of the nose, nasopharynx, and lung, but the evidence for human carcinogenicity has been inconsistent and requires clarification. METHODS: We extended by 11 years the follow-up of an existing cohort of 14 014 men employed after 1937 at six British factories where formaldehyde was produced or used. Subjects had been identified from employment records, and their jobs had been classified for potential exposure to formaldehyde. Standardized mortality ratios (SMRs) were derived using the person-years method and were compared with the expected numbers of deaths for the national population. RESULTS: During follow-up through December 31, 2000, 5185 deaths were recorded, including two from sino-nasal cancer (2.3 expected) and one from nasopharyngeal cancer (2.0 expected). Relative to the national population, mortality from lung cancer was increased among those who worked with formaldehyde, particularly in men in the highest of four estimated exposure categories (>2 ppm) (SMR = 1.58, 95% confidence interval = 1.40 to 1.78), and the increase persisted after adjustment for local geographic variations in mortality (SMR = 1.28, 95% confidence interval = 1.13 to 1.44). However, there was a statistically nonsignificant decrease in the risk of death from lung cancer with duration of high exposure (P(trend) =.18), and this risk showed no trend with time since first high exposure (P(trend) =.99). CONCLUSIONS: The evidence for human carcinogenicity of formaldehyde remains unconvincing. Although a small effect on sino-nasal or nasopharyngeal cancer cannot be ruled out, a possible increase in the risk of lung cancer is a greater concern.
David Coggon (Wed,) studied this question.