Thymic clear cell carcinoma

Definition

A thymic carcinoma composed predominantly or exclusively of clear cells.

Epidemiology

There are only thirteen published cases of pure clear cell carcinoma of the thymus. It may also occur in combination with type A thymoma, squamous cell carcinoma or undifferentiated carcinoma of the thymus.

Clinical features

There is no association with paraneoplastic syndromes.

Macroscopic appearances

Tumour are sometimes encapsulated, sometimes infiltrative.

Histopathology

The clear cells tend to be monotonous and bland, forming solid sheets. Fibrous septa may divide the tumour into lobules. The cytoplasm varies from clear to palely eosinophilic, due to the presence of glycogen in most cases. There is moderate nuclear atypia. There may be focal squamous differentiation. A few lymphocytes may be present.

Immunohistochemistry

	Cytokeratin	1/12
	CK7	may be negative0
	EMA	20% of cases0, 1/12
	CD5	may be positive0, 0/12
	Chromogranin	0/12
	Synaptophysin	0/12
	p53	1/12
	bcl-2	0/12
	PLAP	negative0
	Vimentin	negative0
	CEA	negative0
	S-100	negative0
	CD1a	negative: no immature T-cell component0
	CD99	negative: no immature T-cell component0

Differential diagnosis

Type B3 thymoma with clear cell features.
Metastatic clear cell carcinoma, including renal cell carcinoma, pulmonary carcinoma or thyroid carcinoma.
Mediastinal large B-cell lymphoma.
Mediastinal seminoma.
Mediastinal parathyroid neoplasms.
Clear cell sarcoma or melanoma.
Alveolar rhabdomyosarcoma may have clear cells if glycogen-rich.
Clear cell paraganglioma.

Prognosis

Despite the cytological blandness, these are aggressive tumours.

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 14.1.2006.