title: Malignant peritoneal mesothelioma with a sarcomatoid growth pattern and signet-ring-like structure in a female f344 rat.
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.
authors.affiliation: Laboratory of Pathology, Toxicology Division, The Institute of Environmental Toxicology, 4321 Uchimoriya-machi, Joso, Ibaraki 303-0043, Japan.
authors.forename: Aya
authors.initials: A
authors.lastname: Ohnuma-Koyama
authors.forename: Toshinori
authors.initials: T
authors.lastname: Yoshida
authors.forename: Naofumi
authors.initials: N
authors.lastname: Takahashi
authors.forename: Satoshi
authors.initials: S
authors.lastname: Akema
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Takeuchi-Kashimoto
authors.forename: Maki
authors.initials: M
authors.lastname: Kuwahara
authors.forename: Mika
authors.initials: M
authors.lastname: Nagaike
authors.forename: Kosei
authors.initials: K
authors.lastname: Inui
authors.forename: Nobuaki
authors.initials: N
authors.lastname: Nakashima
authors.forename: Takanori
authors.initials: T
authors.lastname: Harada
keywords: malignant mesothelioma; rat; signet-ring-like structure; spontaneous
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