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. 2022 Feb;50(2):167-175.
doi: 10.1177/01926233211053631. Epub 2021 Nov 2.

Spontaneous Primary Pleural Mesothelioma in Fischer 344 (F344) and Other Rat Strains: A Retrospective Review

Debra A Tokarz  1 , Margarita M Gruebbel  1 , Gabrielle A Willson  1 , Jerry F Hardisty  1 , Gail Pearse  2 , Mark F Cesta  3
Affiliations

Spontaneous Primary Pleural Mesothelioma in Fischer 344 (F344) and Other Rat Strains: A Retrospective Review

Debra A Tokarz et al. Toxicol Pathol. 2022 Feb.

Abstract

Spontaneous primary pleural mesotheliomas in Fischer 344 (F344) or other rat strains have rarely been reported. The objectives of this retrospective study were to develop historical incidence data and better characterize the light-microscopic morphology of these naturally occurring neoplasms in a large cohort of rats of several strains. A retrospective review was performed of National Toxicology Program (NTP) studies in rats conducted between 1980 and 2019 and comprising a total of 104,029 rats (51,326 males, 52,703 females), predominantly (90%) of the F344 strain. Of the 94,062 F344 rats surveyed, there were 30 cases of primary pleural mesotheliomas (22 males, 8 females). Of the 2998 Wistar Han rats surveyed, primary pleural mesotheliomas were present in 2 male rats. No primary pleural mesotheliomas were noted in male and female rats of other strains (6669 Sprague Dawley; 300 Osborne-Mendel). All primary pleural mesotheliomas in control and treated F344 and Wistar Han rats were considered spontaneous and unrelated to treatment. Based on light-microscopic evaluation of paraffin-embedded hematoxylin and eosin stained sections, only epithelioid and biphasic histologic subtypes were observed: 18 and 12 in F344 rats, respectively, and one each in Wistar Han rats. No sarcomatoid subtype cases were noted in any strain of rat.

Keywords: F344; Fischer 344; Wistar Han; mesothelioma; pericardium; pleura; rat.

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Conflict of interest statement

DECLARATION OF CONFLICTING INTEREST STATEMENT

The authors declare no potential, received or perceived conflicts of interest with respect to the research, authorship, and/or publication of this article.

Figures

Figure 1.
Figure 1.
Epithelioid pleural mesothelioma in a male Wistar Han rat (case no. 32). A, Neoplastic masses extend along the pulmonary pleural surface with focal downward compression the underlying pulmonary parenchyma. B-D, Higher magnification regions of the neoplasm shown in A. B, Multifocally the neoplasm forms papillary projections supported by homogenous, pale eosinophilic (hyalinized) collagenous stroma. C, Neoplastic cells also form solid, densely cellular nodules with scant connective tissue stroma. D, Higher magnification of solid nodule in C. Trabeculae composed of cuboidal neoplastic mesothelial cells are supported by scant collagenous stroma. H&E stain.
Figure 1.
Figure 1.
Epithelioid pleural mesothelioma in a male Wistar Han rat (case no. 32). A, Neoplastic masses extend along the pulmonary pleural surface with focal downward compression the underlying pulmonary parenchyma. B-D, Higher magnification regions of the neoplasm shown in A. B, Multifocally the neoplasm forms papillary projections supported by homogenous, pale eosinophilic (hyalinized) collagenous stroma. C, Neoplastic cells also form solid, densely cellular nodules with scant connective tissue stroma. D, Higher magnification of solid nodule in C. Trabeculae composed of cuboidal neoplastic mesothelial cells are supported by scant collagenous stroma. H&E stain.
Figure 1.
Figure 1.
Epithelioid pleural mesothelioma in a male Wistar Han rat (case no. 32). A, Neoplastic masses extend along the pulmonary pleural surface with focal downward compression the underlying pulmonary parenchyma. B-D, Higher magnification regions of the neoplasm shown in A. B, Multifocally the neoplasm forms papillary projections supported by homogenous, pale eosinophilic (hyalinized) collagenous stroma. C, Neoplastic cells also form solid, densely cellular nodules with scant connective tissue stroma. D, Higher magnification of solid nodule in C. Trabeculae composed of cuboidal neoplastic mesothelial cells are supported by scant collagenous stroma. H&E stain.
Figure 1.
Figure 1.
Epithelioid pleural mesothelioma in a male Wistar Han rat (case no. 32). A, Neoplastic masses extend along the pulmonary pleural surface with focal downward compression the underlying pulmonary parenchyma. B-D, Higher magnification regions of the neoplasm shown in A. B, Multifocally the neoplasm forms papillary projections supported by homogenous, pale eosinophilic (hyalinized) collagenous stroma. C, Neoplastic cells also form solid, densely cellular nodules with scant connective tissue stroma. D, Higher magnification of solid nodule in C. Trabeculae composed of cuboidal neoplastic mesothelial cells are supported by scant collagenous stroma. H&E stain.
Figure 2.
Figure 2.
Papillary epithelioid pleural mesothelioma in a male F344 rat (case no. 2). A, Multiple frond-like projections extend from the mesothelial surface (arrowheads) of the mediastinal tissue. B, Higher magnification of A. A characteristic papilliform projection is composed of multiple branching connective tissue trabeculae covered by a single layer of flattened to cuboidal epithelial-type neoplastic mesothelial cells. H&E stain.
Figure 2.
Figure 2.
Papillary epithelioid pleural mesothelioma in a male F344 rat (case no. 2). A, Multiple frond-like projections extend from the mesothelial surface (arrowheads) of the mediastinal tissue. B, Higher magnification of A. A characteristic papilliform projection is composed of multiple branching connective tissue trabeculae covered by a single layer of flattened to cuboidal epithelial-type neoplastic mesothelial cells. H&E stain.
Figure 3.
Figure 3.
Biphasic pleural mesothelioma in a male F344 rat (case no. 28). A, This biphasic mesothelioma contains both papillary epithelioid projections (arrows) and sarcoma-like regions (asterisk). B, Higher magnification of the sarcoma-like region in A. Spindle-shaped neoplastic mesothelial cells with indistinct cell borders form streams and bundles supported by moderate amounts of collagenous stroma. H&E stain.
Figure 3.
Figure 3.
Biphasic pleural mesothelioma in a male F344 rat (case no. 28). A, This biphasic mesothelioma contains both papillary epithelioid projections (arrows) and sarcoma-like regions (asterisk). B, Higher magnification of the sarcoma-like region in A. Spindle-shaped neoplastic mesothelial cells with indistinct cell borders form streams and bundles supported by moderate amounts of collagenous stroma. H&E stain.
Figure 4.
Figure 4.
Epithelioid mesothelioma in a male F344 rat (case no. 10). Psammoma bodies (arrowheads) are scattered within a solid tumor region. H&E stain.
See this image and copyright information in PMC

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