Formaldehyde exposure and respiratory cancer--a meta-analysis of the epidemiologic evidence.

A recent meta-analysis by Blair and his co-workers stimulated the undertaking of a reanalysis of the epidemiologic evidence of an association between formaldehyde and respiratory cancer. Emphasis was placed on extracting the maximal amount of relevant data from the source studies. In close agreement with the original analysis, the aggregated evidence did not indicate an excess risk or an exposure-response gradient for lung cancer. An exposure-response gradient was seen for both sinonasal and nasopharyngeal cancers. The risk for substantial exposure was significantly elevated (odds ratio 1.7 for sinonasal and 2.7 for nasopharyngeal cancer). It is suggested that at least substantial levels of occupational exposure to formaldehyde are associated with a risk of these cancers. The excess risk would be of the order of 100% or more over background rates.