Lung cancer risk following detection of pulmonary scarring by chest radiography in the prostate, lung, colorectal, and ovarian cancer screening trial

Background: Fibrotic scars are frequently found in proximity to lung cancer at the time of cancer diagnosis. However, the nature of the relationship between pulmonary scarring and lung cancer remains uncertain. Our objective was to test whether localized pulmonary scarring is associated with increased lung cancer risk. Methods: Cohort analysis of data from the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. We included 66 863 cancer-free trial participants aged 55 to 74 years, who received a baseline chest radiographic examination and were followed up subsequently for up to 12 years. We used proportional hazards models to estimate hazard ratios (HRs) for lung cancer associated with scarring, adjusting for age, sex, race, and cigarette smoking, and in relation to laterality of scarring. The main outcome measure was incident lung cancer. Results: Scarring was present on the baseline chest radiograph for 5041 subjects (7.5%). Scarring was associated with elevated lung cancer risk (809 lung cancer cases [HR, 1.5; 95% confidence interval {CI}, 1.2-1.8]). This association was specific for cancer in the lung ipsilateral to the scar (HR, 1.8; 95% CI, 1.4-2.4) and absent for contralateral cancer (HR, 0.9; 95% CI, 0.7-1.2). Ipsilateral lung cancer risk was elevated throughout the follow-up period (interval-specific HRs, 1.6, 2.0, 2.1, and 1.7 during 0.01-2.00, 2.01-4.00, 4.01-6.00, and 6.01-12.00 years after baseline chest radiography, respectively). Conclusions: The relationship between pulmonary scarring and lung cancer was specific to the same lung and extended over time. These findings are consistent with the hypothesis that localized inflammatory processes associated with scarring promote the subsequent development of lung cancer.