Thymic spindle cell carcinoma

Definition

This is a spindle cell variant of thymic carcinoma.

Clinical features

All cases in this series were in the anterior mediastinum, without evidence of tumour elsewhere¹.

Macroscopic appearances

These tumours are infiltrative, invading adjacent structures.

Histopathology

There is usually an admixture of conventional spindle cell thymoma and more cellular areas of spindle cells with nuclei showing coarse chromatin and prominent nucleoli and frequent mitoses. There may be vascular invasion. Comedo necrosis is common. There may be some retention of a lobular architecture. The atypical spindle cells may form small nests separated by a desmoplastic stroma. There may variously be foci of lymphoepithelioma-like, squamous or undifferentiated carcinoma.

Immunohistochemistry of the atypical spindle cells:

	Cam5.2	10/101
	broad-spectrum cytokeratin	10/101
	EMA	0/101
	CEA	0/101
	Actin	0/101
	Desmin	0/101
	Vimentin	0/101
	S-100	0/101
	HMB45	0/101
	CD20	0/101
	CD34	0/101
	CD99	0/101
	CD5	2/10 (faint focal positivity)1

Ultrastructure

Differential diagnosis

• Type A thymoma

• Carcinosarcoma: a biphasic tumour in which the spindle cell component is negative for epithelial markers.

• Atypical spindle cell tumours of the mediastinum:

  • leiomyosarcoma

  • synovial sarcoma

  • fibrosarcoma

  • malignant fibrous histiocytoma

  • solitary fibrous tumour

• Metastases:

  • spindle cell carcinoma of the lung

  • sarcomatoid renal cell carcinoma

  • spindle cell melanoma

Prognosis

This is an aggressive tumour, with 5 of 10 patients dying of tumour within 5 years¹.

References

¹Suster, S. and C. A. Moran (1999). "Spindle cell thymic carcinoma: clinicopathologic and immunohistochemical study of a distinctive variant of primary thymic epithelial neoplasm." Am J Surg Pathol 23(6): 691-700.

This page last revised 29.3.2004.

©SMUHT/PW Bishop