Pharyngeal cancer mortality among chemical plant workers exposed to formaldehyde

Objectives: To assess the possible relationship between formaldehyde exposure and mortality risk from pharyngeal cancer ( PC), in particular nasopharyngeal cancer (NPC). Methods: Subjects were 7328 workers employed at a plastics-producing plant (1941-1984). Vital status for 98% of the cohort and cause of death for 95% of 2872 deaths were determined. Reconstructed exposures to formaldehyde, particulates and pigment were used to compute several exposure measures. Standardized mortality ratios (SMRs) were computed for several demographic, work history and formaldehyde exposure variables. In a nested case-control study, seven cases of NPC and 15 cases of other PC were matched on race, sex, age and year of birth to four controls from the cohort. Among interviewed subjects, lifetime smoking history was determined using respondents or proxies for all but one control subject. Results: Statistically significant 2.23-fold and fivefold excesses for PC and NPC, respectively, were observed. Fivefold range NPC excesses were observed for both short (<1 year) and long-term workers and were concentrated among workers hired during 1947-1956. Only three NPC cases were exposed to formaldehyde for longer than one year, and each had low average intensity of formaldehyde exposure (0.03-0.60 ppm). Only a few exposure measures revealed some evidence of an association with all PC or NPC. For all PC combined, adjustment for smoking and year-of-hire in the case-control study generally corroborated findings from the cohort study. Conclusions: Overall, the pattern of findings suggests that the large, persistent nasopharyngeal and other PC excesses observed among the Wallingford workforce are not associated with formaldehyde exposure, and may reflect the influence of nonoccupational risk factors or occupational risk factors associated with employment outside the Wallingford plant.