Myoid Thymoma in F-344 Rats

Neil Allison, DVMDiplomate ACVP

Experimental Pathology Laboratories, Inc

Presented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

Signalment

• Rat, F-344

• Female

• 1.5 year-old

Presented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

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

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

Presented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

Presented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

Presented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

Presented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

Presented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

Presented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

Presented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

Presented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

Presented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

Presented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

Desmin

Presented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

Cytokeratin

Presented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

Diagnosis

• Myoid thymoma

Presented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

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

Discussion• Benign or malignant?

• Gross = Huge and discrete mass

• No invasion of viscera, diaphragm or body wall

• No Metastasis

• Cytology = Malignant

• Behavior = BenignPresented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

Discussion

–Other Names• Carcinosarcoma

• Sarcomatoid carcinoma

Presented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

Acknowledgement• Julie Foley

• Natasha Clayton

• Maureen Puccini

• Emily Singletary

• David Sabio

Presented at SEVPAC 2008 – Permission granted for use on

SEVPAC website only

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