Few population-based studies exist on incidence, risk of infection and mortality in hairy cell leukaemia (HCL).
We used population-based medical databases to identify 209 patients who were diagnosed with HCL in the period from January 1997 to August 2007 in Denmark. An age- and sex-matched comparison cohort of 2,090 persons was selected from the general population. We computed the incidence of HCL using demographic data. Hospitalizations with pneumonia and bacteraemia were determined from the Danish National Patient Registry. Cox regression analysis was used to estimate the relative risk (RR) of infection and mortality ratios (MRR) adjusting for age, sex and comorbidity.
The HCL incidence rates were 1.97 (95% confidence interval 1.51-2.53) and 5.37 (4.57-6.28) per million person-years for women and men, respectively. During a median follow-up of 4.5 years, 48 HCL patients were hospitalized with pneumonia or bacteraemia. The adjusted RR of infection was 8.04 (4.99-12.95) the first year after diagnosis and 1.17 (0.71-1.94) for the remaining follow-up period. The adjusted MRRs were 4.26 (2.61-6.96) and 1.12 (0.75-1.65) the first year after diagnosis and the remaining follow-up period, respectively.
In the second and subsequent years after HCL diagnosis, the risk of infection and mortality was similar to that of the general population.