Temporal variation in the association between benzene and leukemia mortality.
BACKGROUND
Benzene is a human carcinogen. Exposure to benzene occurs in occupational and environmental settings.


OBJECTIVE
I evaluated variation in benzene-related leukemia with age at exposure and time since exposure.


METHODS
I evaluated data from a cohort of 1,845 rubber hydrochloride workers. Benzene exposure-leukemia mortality trends were estimated by applying proportional hazards regression methods. Temporal variation in the impact of benzene on leukemia rates was assessed via exposure time windows and fitting of a multistage cancer model.


RESULTS
The association between leukemia mortality and benzene exposures was of greatest magnitude in the 10 years immediately after exposure [relative rate (RR) at 10 ppm-years = 1.19; 95% confidence interval (CI), 1.10-1.29]; the association was of smaller magnitude in the period 10 to < 20 years after exposure (RR at 10 ppm-years = 1.05; 95% CI, 0.97-1.13); and there was no evidence of association > or = 20 years after exposure. Leukemia was more strongly associated with benzene exposures accrued at > or = 45 years of age (RR at 10 ppm-years = 1.11; 95% CI, 1.04-1.17) than with exposures accrued at younger ages (RR at 10 ppm-years = 1.01; 95% CI, 0.92-1.09). Jointly, these temporal effects can be efficiently modeled as a multistage process in which benzene exposure affects the penultimate stage in disease induction.


CONCLUSIONS
Further attention should be given to evaluating the susceptibility of older workers to benzene-induced leukemia.
Richardson
David B
DB
Department of Epidemiology, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA. david.richardson@unc.edu
D000328:Adult; D000367:Age Factors; D001554:Benzene / Q000633:toxicity*; D002274:Carcinogens, Environmental / Q000633:toxicity*; D002617:Chemical Industry; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007938:Leukemia / Q000139:chemically induced / Q000401:mortality*; D008297:Male; D008875:Middle Aged; D009784:Occupational Diseases / Q000139:chemically induced / Q000401:mortality*; D016273:Occupational Exposure / Q000009:adverse effects*; D013997:Time Factors
D002274:Carcinogens, Environmental; D001554:Benzene