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Published on: October 2, 2015
Spontaneous Primary Pleural Mesothelioma in Fischer 344 (F344) and Other Rat Strains: A Retrospective Review
Debra A Tokarz1, Margarita M Gruebbel1, Gabrielle A Willson1
1Experimental Pathology Laboratories, Research Triangle Park, NC, USA.
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.
Insights
Spontaneous primary pleural mesotheliomas are rare in rats. This study analyzed over 100,000 rats, finding mesotheliomas mainly in Fischer 344 rats, with only epithelioid and biphasic subtypes observed.
Area of Science:
- Veterinary Pathology
- Toxicologic Pathology
- Oncology
Background:
- Spontaneous primary pleural mesotheliomas are infrequently documented in rat models.
- Understanding their incidence and morphology is crucial for toxicological studies.
Purpose of the Study:
- To establish historical incidence data for spontaneous primary pleural mesotheliomas in rats.
- To characterize the light-microscopic morphology of these rare neoplasms.
Main Methods:
- Retrospective review of National Toxicology Program (NTP) rat studies (1980-2019).
- Analysis of 104,029 rats across multiple strains, predominantly Fischer 344 (F344).
- Light-microscopic evaluation of H&E stained tissues from control and treated rats.
Main Results:
- Thirty primary pleural mesotheliomas identified in 94,062 F344 rats (32 per 100,000).
- Two mesotheliomas found in 2,998 Wistar Han rats (67 per 100,000).
- Only epithelioid and biphasic histologic subtypes were observed; no sarcomatoid subtype.
Conclusions:
- Fischer 344 rats exhibit a low incidence of spontaneous primary pleural mesotheliomas.
- The observed neoplasms were spontaneous and not treatment-related.
- Epithelioid and biphasic subtypes are the predominant histologic forms in rats.
