Thymic sarcomatoid carcinoma (carcinosarcoma)

Definition

A thymic carcinoma which is composed wholly or partly of a sarcomatous component.

Synonym

Carcinosarcoma, spindle cell thymic carcinoma

Epidemiology

This tumour accounts for 7% of thymic carcinomas. It occurs in late adulthood.

Macroscopic appearances

The tumour is not encapsulated. There may be necrosis or haemorrhage. There is often invasion of adjacent structures and metastasis to lymph nodes and lung.

Histopathology

The carcinomatous and sarcomatoid components are closely admixed and the carcinomatous component may only be apparent on immunohistochemistry. If morphologically apparent, the carcinomatous component is poorly differentiated with nuclear pleomorphism. There may be squamous differentiation. The sarcomatous component may show skeletal muscle, osteosarcomatous or cartilaginous differentiation. Coagulative necrosis is common.

There may be an associated type A thymoma.

"Spindle cell thymic carcinoma" is probably a variant, the spindle cells showing only epithelial immunoreactivity.

Immunohistochemistry

	Cytokeratin	positive in carcinomatous component, variable in sarcomatoid component0, 3/32
	EMA	positive in carcinomatous component, variable in sarcomatoid component0, 1/32
	CD5	negative0, 0/32
	Chromogranin	0/32
	Synaptophysin	0/32
	bcl-2	2/32
	p53	2/32
	Desmin Actin Myogenin MyoD1	variably positive in rhabdomyosarcomatous component0

Differential diagnosis

Metaplastic thymoma is circumscribed and composed of bland spindle cells.
Sarcoma: a thymic sarcomatoid carcinoma should show areas of carcinomatous differentiation, either morphologically or by electron microscopy or immunohistochemistry. Rhabdomyosarcoma typically occurs in children or young adults. In rhabdomyosarcoma, cells may co-express cytokeratins and myoid markers. In thymic sarcomatoid carcinoma, there should be cells that only express cytokeratins.
Spindle cell carcinoid is usually associated with a conventional carcinoid component. It is positive for neuroendocrine markers.
Synovial sarcoma: the epithelial component is glandular.
Mesothelioma

Prognosis

This is an aggressive tumour with most patient dying within three years.

References

0 Tumours of the Lung, Pleura, Thymus and Heart. WHO Classification of Tumours. IARC Press 2004.

1 J Rosai et al. Histological typing of tumours of the thymus. WHO International histological classification of tumours. Springer-Verlag, second edition, 1999.

2 Chalabreysse, L., B. Etienne-Mastroianni, et al. (2004). "Thymic carcinoma: a clinicopathological and immunohistological study of 19 cases." Histopathology 44(4): 367-74.

This page last revised 11.1.2006.