Understanding LUng Cancer risk factors and their Impact Assessment (LUCIA): protocol for multicentre observational cohort study.

introductionLung cancer (LC) is the leading cause of cancer-related mortality worldwide, primarily due to diagnosis at advanced stages. Although low-dose computed tomography (LDCT) screening reduces lung cancer mortality in high-risk populations, current screening programmes are largely restricted to individuals defined by age and smoking history. This approach excludes never-smokers and individuals with non-smoking-related risk factors, limiting the equity, efficiency and scalability of lung cancer screening. The LUng Cancer risk factors and their Impact Assessment (LUCIA) project aims to overcome these limitations by developing personalised lung cancer risk prediction models and evaluating novel non-invasive technologies for early detection within a risk-adapted screening strategy. METHODS AND ANALYSIS: LUCIA is a multicentre, observational, longitudinal cohort study that will recruit approximately 4000 participants across four European regions: Andalusia and the Basque Country (Spain), Liège (Belgium) and Riga (Latvia). The study population includes smokers, never-smokers and reduced smokers with low-to-moderate lung cancer risk. All participants will initially enter phase 1 (wide population screening) and may transition to phase 2 (precision screening) or phase 3 (diagnosis) based on LDCT findings, results from non-invasive screening devices and artificial intelligence-based risk prediction models. Participants will be followed up for 24 months, with assessments at baseline and at 6, 12 and 24 months. Data collection includes sociodemographic characteristics, medical history, environmental and occupational exposures, lifestyle factors, spirometry, multi-omics profiles and outputs from novel non-invasive devices, including a breath analyser, spectrometry-on-card and a skin-applied volatile organic compound sensing patch. The study will develop and validate integrated lung cancer risk prediction models and evaluate the diagnostic performance of these technologies to support population stratification and personalised screening. ETHICS AND DISSEMINATION: The study will be conducted in accordance with the Declaration of Helsinki, Good Clinical Practice guidelines and applicable national and European regulations. Ethical approval has been obtained from the relevant ethics committees in all participating countries. Written informed consent will be obtained from all participants. Study findings will be disseminated through peer-reviewed open-access publications, scientific conferences and communication with public health stakeholders. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov, NCT06473870.