Medical history, lifestyle, and occupational risk factors for hairy cell leukemia: the InterLymph Non-Hodgkin Lymphoma Subtypes Project.

BackgroundLittle is known about the etiology of hairy cell leukemia (HCL), a rare B-cell lymphoproliferative disorder with marked male predominance. Our aim was to identify key risk factors for HCL.MethodsA pooled analysis of individual-level data for 154 histologically confirmed HCL cases and 8834 controls from five case-control studies, conducted in Europe and Australia, was undertaken. Age-, race and/or ethnicity-, sex-, and study-adjusted odds ratios (OR) and 95% confidence intervals (CI) were estimated using unconditional logistic regression.ResultsThe usual patterns for age and sex in HCL were observed, with a median age of 55 years and sex ratio of 3.7 males to females. Cigarette smoking was inversely associated with HCL (OR = 0.51, 95% CI = 0.37 to 0.71) with dose-response relationships observed for duration, frequency, and lifetime cigarette smoking (P(trend) < .001). In contrast, occupation as a farmer was positively associated with HCL (OR = 2.34, 95% CI = 1.36 to 4.01), with a dose-response relationship observed for duration (OR = 1.82, 95% CI = 0.85 to 3.88 for ≤ 10 years vs never; and OR = 2.98, 95% CI = 1.50 to 5.93 for >10 years vs never; P(trend) = .025). Adult height was also positively associated with HCL (OR = 2.69, 95% CI = 1.39 to 5.29 for upper vs lower quartile of height). The observed associations remained consistent in multivariate analysis.ConclusionsOur observations of an increased risk of HCL from farming exposures and decreased risk from smoking exposures, independent of one another, support a multifactorial origin and an etiological specificity of HCL compared with other non-Hodgkin lymphoma subtypes. The positive association with height is a novel finding that needs replication.