Drug-/radiation-induced interstitial lung disease in the United Kingdom general population: Incidence, all-cause mortality and characteristics at diagnosis

Background and objective: Radiotherapy and an increasing number of substances are implicated in the pathogenesis of interstitial lung disease (ILD). While the frequency of published data on more common ILD entities such as the idiopathic interstitial pneumonias has increased in recent years, less attention has been given to relatively rarely occurring forms such as drug-/radiation-induced ILD. Methods: Data from the UK-based General Practice Research Database (GPRD) was used to estimate the incidence of drug-/radiation-induced ILD over a 12-year period (19972008). Crude incidence rates were stratified by gender, age group and calendar period, and rate ratios were adjusted using Poisson regression. All-cause mortality was modelled using Cox regression, and characteristics at diagnosis were compared with a random sample of matched, non-ILD controls using conditional logistic regression. Results: A total of 128 patients with an incident diagnosis of drug-/radiation-induced ILD were identified, and the overall incidence density during the study period was 4.1 (95% confidence interval 3.44.9) per million person-years. Incidence rates increased during the time period 19972005 and decreased thereafter. The adjusted all-cause mortality was >4 times higher in cases compared with controls. Conclusions: This UK population-based study characterizes patients diagnosed with drug-/radiation-induced ILD and quantifies incidence and all-cause mortality during 19972008. No statistically significant time trend in incidence was found, despite having observed numeric increases in incidence rates during the study window. Future research using the GPRD and other data sources is required to better understand the disposition of patients diagnosed with drug-/radiation-induced ILD and to investigate potential trends incidence and mortality over time.