A thymic carcinoma which is composed wholly or partly of a sarcomatous component.
This tumour accounts for 7% of thymic carcinomas. It occurs in late adulthood.
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.
Cytokeratin |
positive in carcinomatous component, variable in sarcomatoid component0, 3/32 |
||
positive in carcinomatous component, variable in sarcomatoid component0, 1/32 |
|||
negative0, 0/32 |
|||
0/32 |
|||
0/32 |
|||
2/32 |
|||
2/32 |
|||
variably positive in rhabdomyosarcomatous component0 |
|||
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.
This is an aggressive tumour with most patient dying within three years.
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.
This page last revised 11.1.2006.
©SMUHT/PW Bishop