Occupational exposure to formaldehyde and wood dust and nasopharyngeal carcinoma

Objectives-To investigate whether occupational exposures to formaldehyde an d wood dust increase the risk of nasopharyngeal cancer (NPC). Methods-A multicentred, population based case-control study was carried out at five cancer registries in the United States participating in the Nation al Cancer Institute's SEER program. Cases (n=196) with a newly diagnosed NP C between 1987 and 1993, and controls (n=244) selected over the same period from the general population through random digit dialing participated in s tructured telephone interviews which inquired about suspected risk factors for the disease, including a lifetime history of occupational and chemical exposure. Histological type of cancer was abstracted from clinical records of the registries. Potential exposure to formaldehyde and wood dust was ass essed on a job by job basis by experienced industrial hygienists who were b linded as to case or control status. Results-For formaldehyde, after adjusting for cigarette use, race, and othe r risk factors, a trend of increasing risk of squamous and unspecified epit helial carcinomas was found for increasing duration (p=0.014) and cumulativ e exposure (p=0.033) but not for maximum exposure concentration. The odds r atio (OR) for people cumulatively exposed to >1.10 ppm-years was 3.0 (95% c onfidence interval (95% CI) 1.3 to 6.6) compared with those considered unex posed. In analyses limited to jobs considered definitely exposed, these tre nds became stronger. The associations were most evident among cigarette smo kers. By contrast, there was no association between potential exposure to f ormaldehyde and undifferentiated and non-keratinising carcinomas. There was little evidence that exposure to wood dust increased risk of NPC, as modes t crude associations essentially disappeared after control for potential ex posure to formaldehyde. Conclusions-These results support the hypothesis that occupational exposure to formaldehyde, but not wood dust, increases risk of NPC. This associatio n seems to be specific to squamous cell carcinomas. Established cohorts of workers exposed to formaldehyde and wood dust should continue to be monitor ed for NPC and other respiratory cancers. Future studies of NPC should take into account histological type in assessing risk from environmental and ho st factors.