Circulating markers of interstitial lung disease and subsequent risk of lung cancer.

BACKGROUND Inflammation and pulmonary diseases, including interstitial lung diseases, are associated with increased lung cancer risk. Circulating levels of surfactant protein-D (SP-D) and Krebs von Lungren-6 (KL-6) are elevated in interstitial lung disease patients and may be useful markers of processes contributing to lung cancer. METHODS We conducted a nested case-control study, including 532 lung cancer cases, 582 matched controls, and 150 additional controls with chest X-ray (CXR) evidence of pulmonary scarring, in the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial. Serum SP-D and KL-6 levels were measured using enzyme immunoassay. Logistic regression was used to estimate the associations of SP-D and KL-6 with lung cancer and CXR scarring. RESULTS Cases had higher levels than controls for SP-D (median 118.7 vs. 105.4 ng/mL, P = 0.008) and KL-6 (372.0 vs. 325.8 μg/mL, P = 0.001). Lung cancer risk increased with SP-D (P(trend) = 0.0003) and KL-6 levels (P(trend) = 0.005). Compared with the lowest quartile, lung cancer risk was elevated among those with the highest quartiles of SP-D (OR = 1.87, 95% CI: 1.32-2.64) or KL-6 (OR = 1.58, 95% CI: 1.11-2.25). Among controls, participants with CXR scarring were more likely than those without scarring to have elevated levels of SP-D (quartile 4 vs. quartile 1: OR = 1.67, 95% CI: 1.04-2.70, P(trend) = 0.05) but not of KL-6 (OR = 1.04, 95% CI: 0.64-1.68, P(trend) = 0.99). CONCLUSION Circulating levels of SP-D and KL-6 are associated with subsequent lung cancer risk. IMPACT Our findings support a potential role for interstitial lung disease in lung cancer etiology or early detection, but additional research is needed.