Downloaded from oem.bmj.com on December 31, 2012 - Published by group.bmj.com
Short report
Cancer incidence among workers exposed to softwood dust in Lithuania Giedre Smailyte Lithuanian Cancer Registry, Institute of Oncology, Vilnius University, Vilnius, Lithuania Correspondence to Dr Giedre Smailyte, Lithuanian Cancer Registry, Institute of Oncology, Vilnius University, P. Baublio g 3B, Vilnius LT-08406, Lithuania;
[email protected] Accepted 20 November 2011 Published Online First 11 January 2012
ABSTRACT Objectives The aim of this study was to assess cancer incidence in a cohort of woodworkers exposed to softwood dust in a Lithuanian wooden joinery products factory. Methods The study population consisted of 1518 workers (1080 men and 438 women) employed in the factory for at least 1 year between 1947 and 1996 and living in Lithuania on 1 January 1978, when the follow-up for cancer incidence began. The follow-up period for cancer was 1978e2007. Cancer risk was assessed by standardised incidence ratios (SIR) with reference to the national population. Results Overall cancer incidence was not increased among woodworkers. However, the number of mouth and pharynx cancer cases among male woodworkers was significantly increased compared with expected numbers (SIR 2.19, 95% CI 1.17 to 3.74). A higher risk was found for cancer of the buccal cavity than for pharyngeal cancer (SIRs 2.83 and 1.45, respectively). The SIR for larynx cancer was also elevated (SIR 1.39, 95% CI 0.64 to 2.64) among men, while the number of lung cancer cases was higher than expected only among women (SIR 2.07, 95% CI 00.57 to 5.31). Conclusions This results of this study support the hypothesis that exposure to softwood dust may increase the risk of oral and pharyngeal cancer. No support was found for an increased risk of other respiratory cancers among workers exposed to softwood dust.
INTRODUCTION Wood dust has been classified as carcinogenic to humans (group 1) by the International Agency for Research on Cancer (IARC), primarily on the basis of the observation of a marked increase in cancers of the nasal cavities and paranasal sinuses among workers exposed predominantly to hardwood dusts.1 However, about two-thirds of the wood used commercially worldwide is softwood. Unfortunately, the epidemiological data did not distinguish clearly between the different types of wood to which workers were exposed, and there is no separate assessment of the carcinogenic risk related to hard- or softwoods. Only two cohort studies on workers exposed to softwood dust have been published.2 3 One of these studies was conducted in Finland among 1223 sawmill workers followed up from 1945 to 1980.2 Cancer incidence was not in excess overall, and no cases of nasal cancer were found (0.3 expected). In the study from the USA, cancer mortality among 2283 workers employed in plywood mills for at least 1 year was examined.3 Increased cancer risks for multiple myeloma and Hodgkin’s disease were observed, but no nasal cancers were found Occup Environ Med 2012;69:449e451. doi:10.1136/oemed-2011-100253
What this paper adds < Wood dust has been classified as a human
carcinogen due to a marked increase in cancers of the nasal cavities and paranasal sinuses among workers predominantly exposed to hardwood dust. < Most epidemiological studies have examined the risk of cancer among woodworkers exposed to mixed or unspecified wood dust, not softwood dust alone. < The available epidemiological data are insufficient to determine an association between wood dust exposure and an increased risk of cancer other than nasal cancer. < This study of woodworkers exposed to softwood dust in a Lithuanian wooden joinery products factory supports the hypothesis that exposure to softwood dust may increase the risk of oral and pharyngeal cancer.
(expected 0.4 cases). Excesses of various other cancers in these studies were observed, but all results were based on very small numbers. The available epidemiological data are not sufficient to allow definitive assessment of wood dust exposure and increased risk for cancers other than nasal cancer.4 Exposure to softwood dust has been reported to also increase the risk of upper aerodigestive tract and respiratory cancers in some caseecontrol studies.5e7 A census and register based study in five Nordic countries identified an increased risk of nasal cancer among woodworkers mainly exposed to softwood.8 Since it is unclear to what extent softwood dust is associated with cancer risk, cancer incidence was investigated in a cohort of woodworkers exposed to softwood dust in a Lithuanian wooden joinery products factory.
METHODS The factory manufactured joinery products such as wooden windows, doors and floorboards. Pine was the main wood used for production, together with some spruce. Exposure data by different departments were only available for the years 1983 and 1989e1991. The reported means of total dust concentrations in wood-processing departments varied from 1.7 to 23.4 mg/m3. Information for the study population was obtained from employment records. Personal identification data and work history were abstracted for each worker. The inclusion criteria were at least 449
Downloaded from oem.bmj.com on December 31, 2012 - Published by group.bmj.com
Short report 1 year’s employment in the factory between 1947 and 1996 and residence in Lithuania on 1 January 1978, when the follow-up for cancer incidence began. Information on vital status was obtained from the Residents’ Register Service. The cohort consisted of 1518 employees (1080 men and 438 women). By the end of the follow-up on 31 December 2007, 54.8% of workers were alive, 41.3% had died, 3.1% had emigrated and 0.8% had been lost to follow-up. Cancer cases in the cohort were identified in the Lithuanian Cancer Registry by linkage procedures using sex, name and date of birth. Cancer diagnoses were coded according to the WHO 9th Revision of International Classification of Diseases (ICD-9). Standardised incidence ratios (SIR) were calculated as ratios between the observed and expected numbers of cancers.9 The expected numbers were based on sex-specific incidence rates in 5-year age groups and 5-year observation periods for the total Lithuanian population. Follow-up for each individual started after 1 year of total employment for those with first entry after 1 January 1978 and on 1 January 1978 for workers who had reached 1 year of employment before that date. Workers who died or emigrated were followed until the date of these events, while all others were followed until the end of 2007. For workers lost to follow-up during the observation period, person-years were calculated up to the date of discharge from the factory. The cohort contributed 50 444 person-years to the study (34 456 for men and 15 988 for women). Stata V.11.0 was used for analysis. Ethics approval was obtained from the Lithuanian Bioethics Committee.
RESULTS Among male woodworkers, a total of 157 cases of cancer were observed compared to 193.93 expected (SIR 0.81, 95% CI 0.69 to 0.95) (table 1). The number of mouth and pharynx cancer cases among male woodworkers was significantly increased compared to the expected numbers (SIR 2.19, 95% CI 1.17 to 3.74). A higher risk was found for oral cavity cancers than for pharyngeal cancers (SIRs 2.83 and 1.45, respectively). The SIR for larynx
cancer was also elevated (SIR 1.39, 95% CI 0.64 to 2.64), whereas the number of lung cancer cases was no higher than expected (SIR 0.85, 95% CI 0.60 to 1.18). No cancers of the nose and sinuses were observed in this group of male woodworkers (0.47 cases expected). For female workers, the overall incidence of cancer was not increased (SIR 0.88, 95% CI 0.65 to 1.16). The observed numbers of cancers at specific sites were based on a few cases only, however there was one case of oral cavity cancer and four cases of lung cancers rare among women, giving SIRs of 3.75 (95% CI 0.09 to 20.60) and 2.07 (95% CI 00.57 to 5.31), respectively. In addition, an elevated SIR of nose and sinus cancer was observed (SIR 13.88, 95% CI 0.35 to 77.31) because of one case of squamous cell carcinoma of the maxillary sinus (0.07 expected). For respiratory cancers, doseeresponse analyses were conducted using employment duration as an indicator of exposure. No trend for mouth and pharynx, lung and laryngeal cancers among men was observed with increasing duration of employment. The highest risk of lung and laryngeal cancers was found among those employed for
