Malignant peritoneal mesothelioma with a sarcomatoid growth pattern and signet-ring-like structure in a female f344 rat

Our plain-English summary of Malignant peritoneal mesothelioma with a sarcomatoid growth pattern and signet-ring-like structure in a female f344 rat, by A. Ohnuma-Koyama, T. Yoshida, N. Takahashi, et al (Journal of Toxicologic Pathology, 2013).

The study

• Authors: A. Ohnuma-Koyama, T. Yoshida, N. Takahashi, S. Akema, Y. Takeuchi-Kashimoto, M. Kuwahara, M. Nagaike, K. Inui, N. Nakashima, T. Harada
• Journal: Journal of Toxicologic Pathology
• Published: 2013;26(2):197-201
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

We report a biphasic malignant mesothelioma in an aged female F344/DuCrlCrlj rat. Macroscopically, multiple pale brown nodules were observed in the abdominal cavity with retention of bloody ascites. Histopathologically, the tumor cells spread over the peritoneum and formed masses on the surface and underlying adipose tissues. The tumor cells dominantly proliferated in a solid, nodular or nest-like pattern with modest amount of fibrillar connective tissues, which contained hyaluronan. The tumor consisted of ovoid, polygonal or spindle-shaped cells that possessed eosinophilic cytoplasms including glycogen; some tumor cells showed a signet-ring-like structure. Multinucleated cells and mitosis were found frequently, and direct invasion to intra-abdominal organs and intravascular metastasis to the liver were observed. Immunohistochemically, keratin and mesothelin were strongly positive in most of tumor cells, while vimentin was mainly positive in spindle-shaped cells. Podoplanin was also positive, particularly in the cell membrane of tumor cells. Electron microscopically, tumor cells showed an intercellular desmosome-like structure, basement membrane and microvillus. We diagnosed the case as a malignant peritoneal mesothelioma with a sarcomatoid growth pattern and signet-ring-like structure.

In plain English

This case report described a malignant mesothelioma of the peritoneum (the lining of the abdomen) in one aged female F344 laboratory rat. The report did not examine asbestos exposure in this rat. The rat was in a dose group of a carcinogenicity study and ate a diet containing a test chemical that the article does not name. The rat was found dead at 92 weeks of age. At necropsy, many small pale brown nodules, under 5 mm across, were scattered in the abdomen. Under the microscope, the tumor included spindle-shaped cells and cells with a signet-ring-like appearance. It had spread to the liver, pancreas, ovary and diaphragm, including inside liver blood vessels. Most tumor cells stained for keratin and mesothelin, but not for calretinin. Vacuoles inside the cells did not stain for fat. This was the only mesothelial tumor among the treated animals in the study, so the authors considered it spontaneous and not related to the treatment. The authors concluded it was a biphasic malignant mesothelioma with a sarcomatous growth pattern and a signet-ring-like structure.

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, examined by gross pathology, histopathology, immunohistochemistry and electron microscopy)
• Who was studied: one aged female F344/DuCrlCrlj rat in a dose group of a carcinogenicity study in Japan, found dead at 92 weeks of age
• Exposure: No asbestos exposure is described for the rat. The rat was fed a diet containing an unnamed test chemical as part of a carcinogenicity study.
• Main results:
  • At necropsy, multiple pale brown nodules less than 5 mm in diameter were found in the abdominal cavity, with bloody ascites.
  • Under the microscope, parts of the tumor showed proliferation of spindle-shaped cells.
  • Under the microscope, the tumor also showed nest-like proliferation or a signet-ring-like structure.
  • Metastasis was found in the liver, pancreas, ovary and diaphragm.
  • Intravascular metastasis was found in the liver.
  • Most tumor cells reacted positively for keratin.
  • Most tumor cells reacted positively for mesothelin.
  • The tumor cells showed no immunoreactivity for calretinin.
  • The tumor cells were positive for both keratin and vimentin.
  • The tumor cells contained glycogen and produced hyaluronic acid in their stroma.
  • Electron microscopy showed an intercellular desmosome-like structure in the tumor cells.
  • The vacuoles in the tumor cells were negative for Oil Red O stain, meaning they were not fat.
  • This was the only mesothelial tumor among the treated animals in the study. The authors therefore considered it spontaneous and not related to the treatment.
• The authors' conclusion: The authors concluded the tumor was a biphasic malignant mesothelioma with a sarcomatous growth pattern, a signet-ring-like structure and nest-like proliferation, which might mimic a microcystic form of epithelioid mesothelioma in humans.

Topics

Medical terms in this study, explained in our Lexicon: Peritoneal Mesothelioma, Sarcomatoid, Biphasic Mesothelioma, Mesothelioma, Ascites, Peritoneum, Spindle Cell, Eosinophilic.

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