Introduction Studies have suggested that lung cancer is more common in people with idiopathic pulmonary fibrosis (IPF). However, there is limited information on the risk of lung cancer in individuals with connective tissue disease associated pulmonary fibrosis (CTD-PF). The aim of this study was to compare the incidence of lung cancer in people with IPF and CTD-PF with that of the general population.
Methods Using electronic primary care records from The Health Improvement Network (THIN), we identified incident cases of IPF and CTD-PF between 2000 and 2011. For every case of IPF or CTD-PF, up to 4 general population controls matched on age, sex and general practice were randomly selected. We conducted a matched cohort analysis to estimate rate ratios for lung cancer in cases of IPF and CTD-PF compared with matched controls, adjusting for smoking habit.
Results Our study population consisted of 3266 incident cases of IPF, 494 cases of CTD-PF and 14,463 matched general population controls. The majority (64.1%) of people with IPF were male, while most (55.3%) of those with CTD-PF were female. Individuals with CTD-PF were also younger at time of diagnosis compared to people with IPF (mean age at diagnosis 69.0 vs. 74.2 years; p < 0.001). The median follow up time for our study population was 3.1 years (Interquartile range [IQR] 1.3 to 5.6). During this time 80 (2.5%) individuals with IPF, 9 (1.8%) with CTD-PF and 149 (1.0%) controls were diagnosed with lung cancer. After adjusting for smoking and the matching factors, the incidence of lung cancer was higher in people with IPF (Rate Ratio [RR] 3.61, 95% Confidence Interval [CI] 2.44 to 5.34) and CTD-PF (RR 2.35, 95% CI 0.78 to 7.09; p value for trend=0.013) compared to the controls (see Figure 1).
Conclusion Individuals with IPF and CTD-PF are at an increased risk of lung cancer, which cannot be fully explained by smoking habit. With the increasing use of new therapies that may prolong the median survival in individuals with lung fibrosis, our findings raise the possibility these patients may represent a suitable population for lung cancer screening.