Background: The analysis of plasma cell-free DNA (cfDNA) is expected to provide useful biomarkers for early diagnosis of non-small-cell lung cancer (NSCLC). However, it remains unclear whether the intense release of cfDNA into the bloodstream of NSCLC patients results from malignancy or chronic inflammatory response. Consequently, the current diagnostic utility of plasma cfDNA quantification has not been thoroughly validated in subjects with chronic respiratory inflammation. Here we assess the effect of chronic respiratory inflammation on plasma cfDNA levels and evaluate the potential clinical value of this phenomenon as an early lung cancer diagnostic tool.
Methods: We measured plasma cfDNA concentrations in 50 resectable NSCLC patients, 101 patients with chronic respiratory inflammation (chronic obstructive pulmonary disease, sarcoidosis, or asthma) and 40 healthy volunteers using real-time PCR.
Results: We found significantly higher plasma cfDNA levels in NSCLC patients than in subjects with chronic respiratory inflammation and healthy individuals (P<0.0001). There were no significant differences in plasma cfDNA levels between patients with chronic respiratory inflammation and healthy volunteers. The cutoff point of >2.8 ng ml(-1) provided 90% sensitivity and 80.5% specificity in discriminating NSCLC from healthy individuals (area under the curve (AUC)=0.90). The receiver-operating characteristics curve distinguishing NSCLC patients from subjects with chronic respiratory inflammation indicated 56% sensitivity and 91% specificity at the >5.25-ng ml(-1) cutoff (AUC=0.76).
Conclusions: We demonstrated that elevated plasma cfDNA levels in NSCLC resulted primarily from tumour development rather than inflammatory response, raising the potential clinical implications for lung cancer screening and early diagnosis. Further research is necessary to better characterise and identify factors and processes regulating cfDNA levels in the blood under normal and pathological conditions.