Hung YP, Dong F, Dubuc AM, et al. - In a consecutive cohort of 1,110 people with pleural mesotheliomas (a rare solitary circumscribed pleural tumor that is microscopically comparable to diffuse malignant pleural mesothelioma) diagnosed in 2005–2018, the researchers recognized six cases diagnosed with localized pleural mesotheliomas. Two patients were given neoadjuvant chemotherapy. Gross circumscription (with microscopic invasion into lung, soft tissue, and/or rib in four cases), mesothelioma histology (four biphasic and two epithelioid types), and mesothelial immunophenotype was exhibited by every tumor. Three of four patients with at least a 6-month follow-up were alive (up to 8.9 years). Genomic characterization recognized several subgroups ie, BAP1 mutations with deletions of CDKN2A and NF2 in two tumors, TRAF7 mutations in two tumors, including one harboring trisomies of chromosomes 3, 5, 7, and X, and genomic near-haploidization, defined by extensive loss of heterozygosity sparing chromosomes 5 and 7. Localized pleural mesotheliomas seemed genetically heterogeneous and include BAP1-mutated, TRAF7-mutated with near-haploid subgroups. The TRAF7-mutated subgroup overlapped genetically with adenomatoid tumors and well-differentiated papillary mesotheliomas, in which recurrent TRAF7 mutations were reported, while the BAP1-mutated subgroup was comparable to diffuse malignant pleural mesotheliomas. In the pathogenesis of both localized pleural mesothelioma and diffuse malignant pleural mesothelioma, genomic near-haploidization, recognized recently in a subset of diffuse malignant pleural mesotheliomas, recommended a novel mechanism. Thus, with both similarities to and variations from diffuse malignant pleural mesothelioma, distinctive genetic characteristics of localized pleural mesothelioma were explained in this study.