Interstitial lung disease is associated with an increased risk of lung cancer in systemic sclerosis: Longitudinal data from the Canadian Scleroderma Research Group

Objective: The literature supports an increased risk of malignancy in systemic sclerosis, including lung cancer. Our objective was to identify potential independent predictors of lung cancer risk in systemic sclerosis. Methods: We used a cohort of 1560 systemic sclerosis patients from the Canadian Scleroderma Research Group, enrolled from 2004 and followed for a maximum of 11 years. Time to lung cancer was calculated from the onset of the first non-Raynaud's symptoms. Baseline demographic, clinical, and serological characteristics of patients with and without lung cancer were compared. Cox proportional hazards models were used to estimate the effects of demographic variables, exposure to smoking, disease duration, disease subset (diffuse vs limited), immunosuppressant drug exposure, and presence of interstitial lung disease on the risk of lung cancer. Results: Over the 5519 total person-years of follow-up, 18 SSc patients were diagnosed with lung cancer after cohort entry (3.2 cancers per 1000 person-years). In univariate comparisons, cancer cases were more likely to be male, to have a smoking history, and to have interstitial lung disease than non-cases. In multivariate analysis, interstitial lung disease was independently associated with the risk of lung cancer (hazard ratio: 2.95, 95% confidence interval: 1.10-7.87). Conclusion: In addition to known demographic (male sex) and lifestyle risk factors (smoking), interstitial lung disease is an independent risk factor for lung cancer in systemic sclerosis. These results have implications for lung cancer screening in systemic sclerosis.