Abstract
BackgroundTo determine whether the National Cancer Institute’s (NCI) suggestion of a persistent increased mortality risk for nasopharyngeal cancer (NPC) in relation to formaldehyde (FA) exposure is robust with respect to alternative methods of data analysis.MethodsNCI provided the cohort data updated through 2004. We computed U.S. and local county rate-based standardized mortality ratios (SMRs) and internal cohort rate-based relative risks (RR) in relation to four formaldehyde exposure metrics (highest peak, average intensity, cumulative, and duration of exposure), using both NCI categories and alternative categorizations. We modeled the plant group-related interaction structure using continuous and categorical forms of each FA exposure metric and evaluated the impact of NCI’s decision to exclude non-exposed workers from the baseline category.ResultsOverall, our results corroborate the findings of our earlier reanalyses of data from the 1994 NCI cohort update. Six of 11 NPC deaths observed in the NCI study occurred in Plant 1, two (including the only additional NPC death) occurred in Plant 3 among workers in the lowest exposure category of highest peak, average intensity and cumulative FA exposure and in the second exposure category of duration of exposure, and the remaining cases occurred individually in three of eight remaining plants. A large, statistically significant, local rate-based NPC SMR of 7.34 (95 % CI = 2.69–15.97) among FA-exposed workers in Plant 1 contrasted with an 18 % deficit in NPC deaths (SMR = 0.82, 95 % CI = .17–2.41) among exposed workers in Plants 2–10. Overall, the new NCI findings led to: (1) reduced SMRs and RRs in the remaining nine study plants in unaffected exposure categories, (2) attenuated exposure-response relations for FA and NPC for all the FA metrics considered and (3) strengthened and expanded evidence that the earlier NCI internal analyses were non-robust and mis-specified as they did not account for a statistically significant interaction structure between plant group (Plant 1 vs. Plants 2–10) and FA exposure.ConclusionsOur updated reanalysis provided little or no evidence to support NCI’s suggestion of a persistent association between FA exposure and mortality from NPC. NCI’s suggestion continues to be driven heavily by anomalous findings in one study plant (Plant 1).Electronic supplementary materialThe online version of this article (doi:10.1186/s12995-016-0097-6) contains supplementary material, which is available to authorized users.
Highlights
To determine whether the National Cancer Institute’s (NCI) suggestion of a persistent increased mortality risk for nasopharyngeal cancer (NPC) in relation to formaldehyde (FA) exposure is robust with respect to alternative methods of data analysis
We addressed three methodological issues: (Issue 1) inappropriateness of excluding unexposed workers from the evaluation of exposure-response relationships; (Issue 2) the trend tests used in the NCI 2004 updates produce misleading results and may be mis-specified and (Issue 3) failure to recognize the important interaction structure between plant group (i.e., Plant 1 vs. Plants 2–10) and FA exposure reported by Marsh et al [23]
Six of 11 NPC deaths occurred in Plant 1 yielding statistically significant (p < .01) 5.44-fold and 5.57-fold excesses based on the U.S and regional comparisons, respectively
Summary
To determine whether the National Cancer Institute’s (NCI) suggestion of a persistent increased mortality risk for nasopharyngeal cancer (NPC) in relation to formaldehyde (FA) exposure is robust with respect to alternative methods of data analysis. Formaldehyde (FA) is an important industrial chemical. Production in the U.S and the European Union exceeds 10 million tons per year [1]. Adhesives and binders are produced from resins based on FA (e.g., for the manufacture of particle board, paper, and vitreous synthetic fibers), to make plastics and coatings, and FA is used in textile finishing [2]. FA is an intermediate in the production of many chemicals, and as formalin it is used as a disinfectant and preservative. FA is produced in combustion, e.g. in vehicle exhausts and tobacco smoke [2]. FA is formed endogenously in humans [3]
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