Malignant Mesothelioma in the Thoracic Cavity of a Crj:CD(SD) Rat Characterized by Round Hyalinous Stroma

Abstract

Spontaneous malignant mesothelioma was found in a 104-week-old male Crj:CD(SD) rat. The tumor was scattered on the surface of the lung, heart, mediastinal pleura and thoracic wall and metastasized to the alveolar septa. Histopathologically, small flattened or cuboidal tumor cells proliferated with stroma, formed almost normal papillary structures and reacted positively to colloidal iron stain and immunohistochemical staining for mesothelin. Round hyalinous stromata were pronounced, which is a characteristic feature, and the possible reason for this is as follows; at first, a small amount of collagen fibers was formed in the center of the clusters of several tumor cells, and then the cell clusters expanded like balloons with an increase in the collagen fibers.

Malignant Peritoneal Mesothelioma with a Sarcomatoid Growth Pattern and Signet-Ring-Like Structure in a Female F344 Rat

“…As expected, the tumor cells were intensely positive for mesothelin and podoplanin in the present case. Consistent with our findings, several researchers demonstrated that mesothelin and podoplanin were strongly positive in mesothelial cells and/or typical mesothelioma cells in rats 11 , 12 , 13 . The negativity demonstrated for calretinin in our case suggested a species difference in terms of specification of this calcium-binding protein between human and rat mesothelial/mesothelioma cells.…”

Proliferative and Non-Proliferative Lesions of the Rat and Mouse Soft Tissue, Skeletal Muscle and Mesothelium

“…Mesothelin is also considered to be a reliable marker ( 29 Doi et al 2010). Most sarcomatoid mesotheliomas typically stain positively for cytokeratin when a broad-spectrum antibody is used.…”

“…For epithelioid mesothelioma, the most useful markers are broad spectrum cytokeratin, cytokeratin 5/6, cytokeratin 18, Wilm's Tumor-gene 1 WT1 and calretinin ( 60 Kane 2006; 75 Maronpot et al 2009). Mesothelin is also considered to be a reliable marker ( 29 Doi et al 2010). Most sarcomatoid mesotheliomas typically stain positively for cytokeratin when a broad-spectrum antibody is used.…”

Lung, Pleura, and Mediastinum

“…Primary spontaneous pleural mesotheliomas are rare in rats. They have been induced by exposure to various fibers and chemicals (Greaves et al, 2013;Kane, 2006;Doi et al, 2010;Wagner, 1962;Stanton and Wrench, 1972). Grossly, pleural mesotheliomas may be focal or diffuse along the pleura, and grow by expansion rather than infiltration.…”