Mixed Type of Malignant Mesothelioma in an Aged Male ICR Mouse

Our plain-English summary of Mixed Type of Malignant Mesothelioma in an Aged Male ICR Mouse, by M. Shirai, T. Maejima, T. Tanimoto, et al (Journal of Toxicologic Pathology, 2011).

The study

• Authors: M. Shirai, T. Maejima, T. Tanimoto, K. Kumagai, T. Makino, K. Kai, M. Teranishi, A. Sanbuissho
• Journal: Journal of Toxicologic Pathology
• Published: 2011;24(3):169-72
• Type of article: Case report
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Multiple whitish nodules in the thoracic cavity at the site of the thymus were observed in a 101-week-old male ICR mouse. In a histopathological examination, the neoplastic cells were predominantly fusiform in shape and proliferated in sarcomatoid growth patterns. Some neoplastic cells showed epithelial growth patterns, such as the ductal structures. Mitotic figures were frequently seen, and small necrotic foci and invasion to adjacent thoracic organs were noted. In Alcian blue staining, bluish materials were observed between fusiform-shaped cells and in some of the lumens of the ductal structures. In immunohistochemistry, both fusiform-shaped and ductal structure-forming cells were positive for vimentin and weakly positive to positive for cytokeratin. Based on the aforementioned findings, the thoracic nodules were diagnosed as a mixed type of malignant mesothelioma. This case was thought to be rare because of the very low occurrence of spontaneous mesothelioma in mice.

In plain English

This case report described one laboratory mouse: a 101-week-old male ICR mouse in the control group of a 2-year carcinogenicity study, which had received 0.5% carboxymethyl cellulose by gavage. The article does not describe any asbestos exposure, and the authors treated the tumor as spontaneous. At necropsy, several whitish nodules about 2 mm across were found in the chest at the site of the thymus. There was also an enlarged mediastinal lymph node and about 0.8 mL of clear fluid in the chest. Under the microscope, the tumor cells were mostly spindle-shaped (sarcomatoid), with some areas forming duct-like epithelial structures. The cells divided frequently and spread into nearby chest tissues, but no similar lesions were seen outside the chest. The cells stained positive for vimentin and weakly positive to positive for cytokeratin, and negative for S-100, alpha-SMA and desmin. A separate lung tumor (bronchioloalveolar carcinoma) was also found, and the authors judged it unrelated. The authors diagnosed a mixed type of malignant mesothelioma and concluded that it was a rare spontaneous case.

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, pathology examination)
• Who was studied: One 101-week-old male ICR mouse from the control group of a 2-year carcinogenicity study at a company laboratory in Japan
• Exposure: No asbestos exposure is described. The mouse was a control animal given 0.5% carboxymethyl cellulose by gavage, and the tumor was considered spontaneous.
• Main results:
  • At necropsy, multiple whitish nodules about 2 mm in diameter were found in the thoracic cavity at the site of the thymus, some adhered to the thoracic wall
  • The mediastinal lymph node was enlarged, and about 0.8 mL of clear fluid was present in the chest (hydrothorax)
  • The tumor cells were predominantly sarcomatoid (spindle-shaped), with an epithelial growth pattern in part, including ductal structures
  • Mitotic figures were frequent and small necrotic foci were present; no similar lesions were found in organs outside the chest
  • The tumor cells, including those with epithelial patterns, were positive for vimentin and weakly positive to positive for cytokeratin, and negative for S-100, alpha-SMA and desmin
  • A bronchioloalveolar carcinoma was found in the cranial lobe of the right lung but was judged unrelated to the chest tumor, with no direct continuity between them
• The authors' conclusion: The authors concluded that the chest nodules were a mixed type of malignant mesothelioma and that this was a rare spontaneous mesothelioma in a mouse

Topics

Medical terms in this study, explained in our Lexicon: Mesothelioma, Sarcomatoid, Immunohistochemistry.

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• Keratin protein immunoreactivity of sarcomatoid and mixed types of diffuse malignant mesothelioma: an immunoperoxidase study of 30 cases — A.G. Montag, G.S. Pinkus, et al. (1988)
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