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

Our plain-English summary of Malignant Mesothelioma in the Thoracic Cavity of a Crj:CD(SD) Rat Characterized by Round Hyalinous Stroma, by T. Doi, Y. Kotani, K. Takahashi, et al (Journal of Toxicologic Pathology, 2010).

The study

• Authors: T. Doi, Y. Kotani, K. Takahashi, S. Hashimoto, N. Yamada, H. Kokoshima, Y. Tomonari, Y. Wako, M. Tsuchitani
• Journal: Journal of Toxicologic Pathology
• Published: 2010;23(2):103-6
• Type of article: Case report
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

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.

In plain English

This was a case report of one male Crj:CD(SD) (Sprague-Dawley) laboratory rat that died at 104 weeks of age. It was one of 200 rats of both sexes in a two-year background data study for cancer testing, and it was given methylcellulose solution by mouth. The article reports no asbestos or other fiber exposure for this rat, and the authors called the tumor spontaneous. At necropsy the rat had about 30 mL of red fluid in the chest and many small whitish or brownish masses on the thoracic wall, lung, heart, mediastinal pleura and diaphragm. The authors reported that the tumor had spread (metastasized) to the lung's alveolar septa. Findings under the microscope and electron microscope, including positive staining for mesothelin, supported the authors' diagnosis of malignant mesothelioma. The tumor's characteristic feature was small, round, collagen-rich (hyalinous) stroma, some with psammoma bodies at their centers. Mesothelioma occurred only in this rat in the study. The authors suggested that the usual tumor site may differ between Sprague-Dawley and Fischer 344 rats. A single case does not show how often such tumors occur.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: case report (single animal, gross, histopathological and electron microscopic description)
• Who was studied: one male Crj:CD(SD) rat, one of 200 specific-pathogen-free rats of both sexes from Charles River Japan, studied at a laboratory in Ibaraki, Japan; died at 104 weeks of age
• Exposure: No asbestos or fiber exposure is reported for this rat. The affected rat was given oral methylcellulose solution as part of a 2-year background data study, and the tumor was described as spontaneous.
• Main results:
  • Before death at 104 weeks the rat showed emaciation, hunched posture, reduced activity, rapid breathing and low body temperature
  • At necropsy about 30 mL of red pleural effusion was found
  • Numerous small whitish or brownish masses were scattered on the thoracic wall, lung, heart, mediastinal pleura and diaphragm
  • The authors reported that tumor cells metastasized to the alveolar septa of the lung
  • Mitotic figures were infrequent
  • The stroma was mostly hyalinous, small and round, which was the characteristic feature of this case
  • Psammoma bodies were seen at the centers of some of the characteristic stromata
  • Most tumor cells stained positively for mesothelin
  • Under the electron microscope, tumor cells had numerous surface microvilli and intercellular junctions
  • Mesothelioma occurred only in this one rat in the background data study
• The authors' conclusion: The authors concluded that the findings indicated malignant mesothelioma arising in the mesothelium of the thoracic organs or tissues. They suggested that the preferred site for mesothelioma may differ between Sprague-Dawley and Fischer 344 rats. They proposed that the round stroma formed as tumor cell clusters expanded like balloons around growing collagen.
• Limitations the authors state:
  • The exact primary site of the tumor could not be determined

Topics

Medical terms in this study, explained in our Lexicon: Mesothelioma, Pleura, Iron Stain (Prussian Blue), Immunohistochemistry, Mesothelin, Collagen.

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