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Updated: May 9, 2026
Orthotopic Implantation and Peripheral Immune Cell Monitoring in the II-45 Syngeneic Rat Mesothelioma Model
Published on: October 2, 2015
Malignant peritoneal mesothelioma with a sarcomatoid growth pattern and signet-ring-like structure in a female f344
Aya Ohnuma-Koyama1, Toshinori Yoshida, Naofumi Takahashi
1Laboratory of Pathology, Toxicology Division, The Institute of Environmental Toxicology, 4321 Uchimoriya-machi, Joso, Ibaraki 303-0043, Japan.
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.
Insights
This study details a rare biphasic malignant mesothelioma in an aged rat, characterized by peritoneal spread and sarcomatoid features. The findings contribute to understanding rare tumor presentations in animal models.
Area of Science:
- Veterinary Pathology
- Oncology
- Animal Models
Background:
- Malignant mesothelioma is a rare tumor arising from mesothelial cells.
- Biphasic mesothelioma exhibits both epithelial and sarcomatous components.
- Animal models are crucial for studying mesothelioma pathogenesis and treatment.
Purpose of the Study:
- To report and characterize a case of biphasic malignant mesothelioma in an aged female rat.
- To describe the macroscopic, histopathological, immunohistochemical, and ultrastructural features of the tumor.
- To contribute to the understanding of mesothelioma in non-human models.
Main Methods:
- Macroscopic examination of the abdominal cavity.
- Histopathological analysis of tumor tissues.
- Immunohistochemical staining for keratin, mesothelin, vimentin, and podoplanin.
- Electron microscopy for ultrastructural evaluation.
Main Results:
- A biphasic malignant mesothelioma was identified in the abdominal cavity with peritoneal spread.
- Tumor cells exhibited solid, nodular, or nest-like proliferation with sarcomatoid features and signet-ring-like structures.
- Immunohistochemistry confirmed expression of keratin, mesothelin, vimentin, and podoplanin.
- Electron microscopy revealed desmosome-like structures, basement membrane, and microvilli.
Conclusions:
- The case represents a malignant peritoneal mesothelioma with a sarcomatoid growth pattern and signet-ring-like structures.
- The findings highlight the importance of detailed pathological characterization in animal models.
- This report adds to the knowledge base of rare neoplasms in laboratory animals.
