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Objectives To assess key elements of the design for Meso-ORIGINS (Mesothelioma Observational study of RIsk prediction and Generation of paired benign-meso tissue samples, Including a Nested MRI Substudy), an ambitious, UK-wide, prospective study that will collect ≥63 matched benign-mesothelioma tissue pairs through longitudinal surveillance and repeat biopsy of patients with asbestos-associated pleural inflammation (AAPI).Design A multicentre, mixed-methods feasibility study, comprising a prospective observational element, evaluating recruitment feasibility, technical feasibility of repeat local anaesthetic thoracoscopy (LAT) and patient acceptability, and a retrospective cohort study focused on AAPI-mesothelioma evolution rate, informing sample size.Setting 4 UK pleural disease centres (February 2019–January 2020).Participants Patients with AAPI (history or typical imaging plus appropriate pleural histology) were eligible for both elements. In August 2019, eligibility for the prospective element was broadened, including addition of radiological AAPI for technical feasibility and patient acceptability endpoints only. Retrospective cases required ≥2 years follow-up.Outcome measures A prospective recruitment target was set a priori at 27 histological AAPI cases (or 14 in any 6 months). Technical feasibility and patient acceptability were determined at 6-month follow-up by thoracic ultrasound surrogates and questionnaires, respectively. Retrospective malignant pleural mesothelioma evolution rate was defined by proportion (95% CI). Baseline predictors of evolution were identified using logistic regression.Results 296 patients with AAPI (39 prospective, 257 retrospective) were recruited/selected. 21/39 prospective recruits were histologically diagnosed (target n=27). Repeat LAT was technically feasible and acceptable in 13/28 (46%) and 24/36 (67%) cases with complete follow-up data. Mesothelioma evolution was confirmed histologically in 36/257 retrospective cases (14% (95% CI 10.3% to 18.8%)) and associated with malignant CT features (OR 4.78 (95% CI 2.36 to 9.86)) and age (OR 1.06 (95% CI 1.02 to 1.12)).Conclusions Our initial eligibility criteria were too narrow. Meso-ORIGINS will recruit a broader cohort, including prevalent cases, any biopsy type and patients with malignant CT features. A range of rebiopsy techniques will be allowed, accounting for technical and patient factors. The sample size has been reduced to 500.Trial registration number ISRCTN12840870.