2.2. Inclusion and Exclusion Criteria

The review included only studies in which the participants were classified as “exposed to formaldehyde.” The exposure assessment was considered acceptable if performed by direct (personal or environmental) sampling of FA, occupational history data, or job exposure matrix. Cancers were classified using the International Classification of Diseases, Tenth Revision (ICD-10).

Only studies involving humans (men and/or women) exposed to FA in occupational settings, reporting results for any kind of cancer and published in peer-reviewed journals, were selected. Searches providing no information about the exposure assessment method or with a self-assessment by the participants were excluded. Besides, we excluded reviews, editorial articles, individual contributions (i.e., conference speeches), and purely descriptive studies published in scientific conferences without any quantitative or qualitative conclusions. Finally, articles published in languages other than English were excluded.