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Background: Mesothelioma is histologically divided into three subgroups: epithelioid, sarcomatoid, and biphasic types. The epithelioid or sarcomatoid type is morphologically defined by polygonal or spindle-like forms of cells, respectively. The biphasic type consists of both components. It is not yet understood how histological differentiation of mesothelioma is regulated. ERC/mesothelin is expressed in most cases of the epithelioid type, but not in the sarcomatoid type of mesothelioma. Consequently, its expression is well correlated to the histological subtype. We hypothesized that ERC/mesothelin expression influences the histological differentiation of mesothelioma, and tested this hypothesis.Methods: We performed studies using the overexpression or knockdown of ERC/mesothelin in mesothelioma cells to examine its effect on cellular morphology, growth kinetics, or migration/invasion activity, in vitro. We then transplanted ERC/mesothelin-overexpressing and control cells into the intraperitoneal space of mice. We examined the effect of ERC/mesothelin overexpression on mouse survival and tumor phenotype.Results: In vitro cell culture manipulations of ERC/mesothelin expression did not affect cellular morphology or proliferation, although its overexpression enhanced cellular adhesion and the migration/invasion activity of mesothelioma cells. The survival rate of mice following intraperitoneal transplantation of ERC/mesothelin-overexpressing mesothelioma cells was significantly lower than that of mice with control cells. The histological evaluation of the tumors, however, did not show any morphological difference between two groups, and our hypothesis was not validated. Unexpectedly, both groups (ERC/mesothelin-overexpressing and control) of mesothelioma cells that were morphologically monophasic and spindle-like in vitro differentiated into a biphasic type consisting of polygonal and spindle-like components in the transplanted tumor, irrespective of ERC/mesothelin expression.Conclusions: These results suggested that the histological transition of mesothelioma between epithelioid and sarcomatoid types may be reversible and regulated not by ERC/mesothelin, but by other unknown mechanisms. [ABSTRACT FROM AUTHOR]

Primary malignant pericardial sarcomatoid mesothelioma (PMPSM) is an extremely rare tumor with poor prognosis. We present an autopsy case in an 80-year-old man admitted for heart failure after one month of treatment at an outpatient clinic. He died three months after symptom onset. A complete autopsy revealed localization of the tumor to the pericardium without other lesions. Histologically, mainly spindle-shaped atypical cells with hyperchromatic nuclei and nucleoli were observed. Immunohistochemical markers for mesothelioma were positive for calretinin, cytokeratin AE1/AE3, and cytokeratin CAM5.2. Thus, we diagnosed primary sarcomatoid malignant mesothelioma of the pericardium. To our knowledge, only four PMPSM cases have been reported in the English literature in the past 30 years. Although PMPSM is rare, clinicians and pathologists should recognize it as a possible diagnosis of pericardial tumors. It is necessary to accumulate clinical and pathological diagnostic findings to establish early detection methods for this extremely rare disease. [ABSTRACT FROM AUTHOR]

A 56-year-old man underwent extrapleural pneumonectomy for malignant pleural mesothelioma (MPM). The histological diagnosis was epithelioid mesothelioma with T2N0M0, and no sarcomatoid component was observed. Subsequently, 14 years after complete resection, screening computed tomography detected a rapidly growing right thoracic mass, which was diagnosed as a recurrence of MPM on resection. However, it was composed of both epithelioid (50%) and sarcomatoid (50%) components, suggesting possible histological transformation. Although there have been some previous reports on the recurrence of MPM, to the best of our knowledge, this is the first clinical case which indicated that histological transformation of MPM might occur. [ABSTRACT FROM AUTHOR]