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Objective: To provide the most up-to-date data on the burden of malignant mesothelioma (MM) and the projections through 2029 in China. Methods: Data on patients diagnosed with MM from China during 1990–2019 were obtained from the Global Burden of Disease (GBD) 2019 database, including annual cases and deaths data and age-standardized rates of incidence, mortality, and disability-adjusted life-years (DALYs) associated with MM among different age groups. Temporal trends during 1990–2019 were analyzed by the Joinpoint regression models using 95% confidence interval (CI), while the projections through 2029 were calculated by the Bayesian age-period-cohort model. Data on the production and consumption of asbestos in China were obtained from the United States Geological Survey on Mineral Commodity Summaries during 1996–2023. Results: We observed a significant elevation in incident new cases and deaths over the last 3 decades, increasing from 1193 in 1990 to 2815 in 2019 for incident cases and from 1134 in 1990 to 2773 in 2019 for death cases. We found a roughly 6% increase in the proportion of incident cases for those aged >70 years (30% in 2019 versus 24% in 1990), while for the proportion of deaths similar elevation for those aged >70 years was found. Additionally, men had significantly higher DALYs due to MM across age groups compared with women. Asbestos consumption in China dramatically dropped since 2012 and reached the bottom in 2017 with 230 kilotons. By 2029, the projected age-standardized rate for incidence and mortality is expected to reach 1.2 per million for both. Conclusion: We found, for the first time using GBD data on the Chinese population, that the burden of MM has been significantly increasing in China over the last three decades and will continue to increase in the upcoming decade, suggesting an urgent need for a complete ban on chrysotile asbestos in China.

Background: Malignant pleural mesothelioma (MPM) is an aggressive cancer related to asbestos exposure. Early diagnosis is challenging due to generic symptoms and a lack of biomarkers. We previously demonstrated that mesothelial precursor cells (MPC) characterized by mesothelin (MSLN)+CD90+CD34+ could be implicated in the development of mesothelioma after asbestos exposure. Here, we aimed to determine the clinical significance of detecting MPC in blood for early-stage diagnosis and prognosis of mesothelioma. Methods: Due to the rarity of MPC in blood, it is challenging to identify this cell population using conventional techniques. Hence, we have developed a microfluidic liquid biopsy platform called MesoFind that utilizes an immunomagnetic, mesothelin capture strategy coupled with immunofluorescence to identify rare populations of cells at high sensitivity and precision. To validate our technique, we compared this approach to flow cytometry for the detection of MPC in murine blood and lavage samples. Upon successful validation of the murine samples, we then proceeded to examine circulating MPC in 23 patients with MPM, 23 asbestos-exposed individuals (ASB), and 10 healthy donors (HD) to evaluate their prognostic and diagnostic value. Finding: MPC were successfully detected in the blood of murine samples using MesoFind but were undetectable with flow cytometry. Circulating MPC were significantly higher in patients with epithelioid MPM compared to HD and ASB. The MPC subpopulation, MSLN+ and CD90+, were upregulated in ASB compared to HD suggesting an early role in pleural damage from asbestos. The MPC subpopulation, MSLN+ and CD34+, in contrast, were detected in advanced MPM and associated with markers of poor prognosis, suggesting a predominant role during cancer progression. Interpretation: The identification of circulating MPC presents an attractive solution for screening and early diagnosis of epithelioid mesothelioma. The presence of different subtypes of MPC have a prognostic value that could be of assistance with clinical decisions in patients with MPM. Funding: Princess Margaret Hospital Foundation Mesothelioma Research Fund, Toronto General & Western Hospital Foundation.

Summary: Malignant mesothelioma (MM) is an aggressive neoplasm characterized by a poor patient survival rate, because of rapid tumor recurrence following first-line therapy. Cancer stem cells (CSCs) are assumed to be responsible for initiating tumorigenesis and driving relapse after therapeutic interventions. CSC-enriched MM cell subpopulations were identified by an OCT4/SOX2 reporter approach and were characterized by (1) increased resistance to cisplatin, (2) increased sensitivity toward the FAK inhibitor VS-6063 in vitro, and (3) a higher tumor-initiating capacity in vivo in orthotopic xenograft and allograft mouse models. Overexpression of NF2 (neurofibromatosis 2, merlin), a tumor suppressor often mutated or lost in MM, did not affect proliferation and viability of CSC-enriched MM populations but robustly decreased the viability of reporter-negative cells. In contrast, downregulation of calretinin strongly decreased proliferation and viability of both populations. In summary, we have enriched and characterized a small MM cell subpopulation that bears the expected CSC characteristics. : A cancer stem cell (CSC)-enriched malignant mesothelioma (MM) cell subpopulation was identified by an OCT4/SOX2 reporter approach. These EGFP-expressing cells showed an altered sensitivity toward chemotherapeutic drugs and a higher tumor-initiating capacity in vivo in orthotopic xenograft and allograft mouse models. While NF2 overexpression had no effect on proliferation/viability of CSC-enriched MM populations, they were susceptible to downregulation of calretinin. Keywords: mesothelioma, cancer stem cells, SOX2, OCT4, NF2, merlin, calretinin, defactinib