CT screening of lung cancer brings forward early disease. The danish lung cancer screening trial (DLCST): Status after five years of CT screening

Background: The effects of low dose CT screening on true disease stage-shift, mortality and overdiagnosis are unclear. We present lung cancer findings and mortality at end of screening in the randomised Danish Lung Cancer Screening Trial (DLCST). Methods: 4,104 men and women, healthy heavy smokers/former smokers were randomised to annual low dose CT screening or no screening for five years (baseline and four incidence rounds). Two experienced chest radiologists read all CT scans and registered the location, size and morphology of nodules. Nodules with a diameter between 5 and 15 mm without benign characteristics were rescanned after three months. Volume-doubling-time (VDT) was used to measure growth rate. Growing nodules (>25% increase in volume) and nodules larger than 15 mm were referred for diagnostic workup. In the control group, lung cancers were diagnosed and treated outside the study by usual clinical practice. Results: The participation rates were high in both groups (screen: 95.5%; control 93.0%; p<0.001). 2.5% of screening tests were positive, and after diagnostic workup 1.8% were classified as false positive findings (non-malignant). Lung cancer detection rate was 0.8% at baseline and mean annual detection rate was 0.6% at incidence rounds (p=0.492). Significantly more lung cancers were diagnosed in the screening group as compared to the control group (68 vs.24, p<0.001), and more were low stage (57 vs.10 stage I-IIIA NSCLC and limited stage SCLC, p<0.001), whereas frequencies of high stage were the same (11 vs.14 stage IIIB-IV NSCLC and extensive stage SCLC, p=0.640). This indicates no absolute stage-shift and some degree of overdiagnosis. At end of screening, 60 were deceased in the screening group and 42 in the control group (p=0.072). 15 and 10 died of lung cancer, respectively (p=0.923). Conclusion: CT screening of lung cancer brings forward early disease, and at this point no absolute stage-shift or reduction in mortality was observed. Significantly more lung cancers were diagnosed in the screening group indicating some degree of overdiagnosis.