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Myoid Thymoma in F-344 Rats

Myoid Thymoma in F-344 Rats. Neil Allison, DVM Diplomate ACVP Experimental Pathology Laboratories, Inc. Signalment. Rat, F-344 Female 1.5 year-old. History. National Toxicology Program (NTP) chronic carcinogenesis study Thin, ataxic and breathing abnormally on day 526 of the study

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Myoid Thymoma in F-344 Rats

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  1. Myoid Thymoma in F-344 Rats Neil Allison, DVM Diplomate ACVP Experimental Pathology Laboratories, Inc Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  2. Signalment • Rat, F-344 • Female • 1.5 year-old Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  3. History • National Toxicology Program (NTP) chronic carcinogenesis study • Thin, ataxic and breathing abnormally on day 526 of the study • Euthanasia Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  4. Necropsy Findings • Cranial mediastinal mass • Discrete, oval, mottled • 40 x 32 x 25 mm Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  5. Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  6. Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  7. Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  8. Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  9. Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  10. Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  11. Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  12. Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  13. Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  14. Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  15. Desmin Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  16. Cytokeratin Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  17. Diagnosis • Myoid thymoma Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  18. Discussion • Reviewed all thymomas in NTP • Data from 1972-2003 • Approximately 189,500 F344 rats • 4/244 thymomas with myoid component • One myoid thymoma after 2003 Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  19. Discussion • Benign or malignant? • Gross = Huge and discrete mass • No invasion of viscera, diaphragm or body wall • No Metastasis • Cytology = Malignant • Behavior = Benign Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  20. Discussion • Other Names • Carcinosarcoma • Sarcomatoid carcinoma Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  21. Acknowledgement • Julie Foley • Natasha Clayton • Maureen Puccini • Emily Singletary • David Sabio Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

  22. References • 1. Snover MS , Levine GD, Rosai J: Thymic carcinoma. Five distinct histological variants. Am j Surg Pathol 6:451-470, 1982 • 2. Rosai J, Sobin LH: Histological typing of tumours of the thymus. In: World Health Organisation, International Histological Classification of Tumours, 2nd ed., pp.1-58. Springer, Berlin, Germany, 1999 • 3. Henry K: An unusual tumour with a striated muscle (myoid) component (with a brief review of the literature on myoid cells). Brit J Dis Chest 66:291-299, 1972 • 4. Murakami S, Shamoto M, Miura K, Takeuchi J: A thymic tumor with massive proliferation of myoid cells. Acta Pathol Jpn 34:1375-1383, 1984 • 5. Pearse G: Histopathology of the thymus. Toxicol Pathol 34:515-547, 2006 Presented at SEVPAC 2008 – Permission granted for use on SEVPAC website only

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