BACKGROUND: Debate about the optimal lung cancer screening strategy is ongoing. In this study, previous screening history of the Dutch-Belgian Lung Cancer Screening trial (NELSON) is investigated on if it predicts the screening outcome (test result and lung cancer risk) of the final screening round.METHODS: 15 792 participants were randomised (1:1) of which 7900 randomised into a screening group. CT screening took place at baseline, and after 1, 2 and 2.5 years. Initially, three screening outcomes were possible: negative, indeterminate or positive scan result. Probability for screening outcome in the fourth round was calculated for subgroups of participants.RESULTS: Based on results of the first three rounds, three subgroups were identified: (1) those with exclusively negative results (n=3856; 73.0%); (2) those with ≥1 indeterminate result, but never a positive result (n=1342; 25.5%); and (3) with ≥1 positive result (n=81; 1.5%). Group 1 had the highest probability for having a negative scan result in round 4 (97.2% vs 94.8% and 90.1%, respectively, p<0.001), and the lowest risk for detecting lung cancer in round 4 (0.6% vs 1.6%, p=0.001). 'Smoked pack-years' and 'screening history' significantly predicted the fourth round test result. The third round results implied that the risk for detecting lung cancer (after an interval of 2.5 years) was 0.6% for those with negative results compared with 3.7% of those with indeterminate results.CONCLUSIONS: Previous CT lung cancer screening results provides an opportunity for further risk stratifications of those who undergo lung cancer screening.TRIAL REGISTRATION NUMBER: Results, ISRCTN63545820.

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Keywords Clinical Epidemiology, Lung Cancer, Smoking cessation, Tobacco and the lung
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Journal Thorax: an international journal of respiratory medicine
Yousaf-Khan, A.U, van der Aalst, C.M, de Jong, P.A, Heuvelmans, M.A, Scholten, E.T, Walter, J. (Joan), … de Koning, H.J. (2017). Risk stratification based on screening history: the NELSON lung cancer screening study. Thorax: an international journal of respiratory medicine, 72(9), 819–824. doi:10.1136/thoraxjnl-2016-209892