Abstract
In 2009, a working group of the International Agency for Research on Cancer classified formaldehyde as carcinogenic to humans (Group 1) and concluded that formaldehyde causes cancer of the nasopharynx (NPC) and leukemia. The results of a large cohort study of industrial workers exposed to formaldehyde, conducted by the U.S. National Cancer Institute, mainly contributed to the available body of epidemiologic evidence. In their recent updated re-analysis of these cohort data published in your journal, Dr Marsh and his colleagues concluded that the results of the original analysis of NPC-risk are misleading because they are based on inappropriate regression analyses. In our view the reason for the elevated NPC risk reported in the original analysis might be also another one - a diagnostic bias. Therefore, it would be very helpful if the authors provided results for all other sub-categories (as three-digit categories of the International Classification of Diseases) of the pharynx to verify the hypothesis described and, hence, to clarify the relationship between exposure to formaldehyde and the risk of NPC.