New insights into the mortality risk from nasopharyngeal cancer in the national cancer institute formaldehyde worker cohort study.

Background: Indications were found that a diagnostic bias could have contributed to the National Cancer Institute's (NCI) suggestion of a persistent increased mortality risk for nasopharyngeal cancer (NPC). Methods: NCI provided the cohort data updated through 2004. We computed local county rate-based standardized mortality ratios (SMRs) for NPC and all other entities of the pharynx for two time periods. Moreover, SMRs were calculated for pharyngeal cancer in relation to study site by cumulative exposure to formaldehyde (FA). Results: Overall, our results corroborate the indications of a diagnostic bias by strong but contrary temporal trends for NPC and pharynx, not specified. Moreover, it was shown that mortality risks were increased in the Wallingford cohort for all pharyngeal cancer combined and for pharyngeal cancer excluding NPC. In contrast, no increased risks for these categories were found in the nine other study sites combined. Conclusions: Our re-analysis provided little or no evidence to support NCI's suggestion of a persistent association between FA exposure and mortality from NPC. [ABSTRACT FROM AUTHOR]