Thymic carcinoid tumour, well-differentiated thymic neuroendocrine carcinoma

Alomst all carcinoids of the thymus fulfil the criteria for atypical carcinoids.

Clinical features

There is an association with MEN I and with Cushing syndrome2,3. Almost all MEN-associated cases occur in men. Carcinoid syndrome is very rare.

Histopathology

This is a well-differentiated tumour composed of a uniform population of cells forming nests, ribbons, festoons and glands.

Classic carcinoid: polygonal cells have granular amphophilic cytoplasm.
Spindle cell carcinoid: appearances are as for spindle cell carcinoid of lung.
Pigmented carcinoid: tumour cells and histiocytes contain melanin.
Oncocytic/oxyphilic carcinoid.
Mucinous carcinoid
Angiomatoid carcinoid.
Carcinoid with sarcomatous change.
With amyloid: the tumour cells are positive for calcitonin and there is amyloid deposition in the stroma, making this tumour indistinguishable from medullary carcinoma of the thyroid.
Atypical carcinoid shows a mitotic count of 2 to 10 per 2 mm3 (10 HPF) and necrosis. The proportion of carcinoid fulfilling this criterion is greater than for pulmonary carcinoids.
"Paraganglioid" carcinoid includes S-100 positive sustentacular cells3.

Some cases arise from germ cell tumours4.

Immunohistochemistry

	Typical carcinoid	atypical carcinoid
Cytokeratin		11/123, 3/35
EMA		1/35
Chromogranin	3/3 (one case only weak)2	5/62, 3/35
Synaptophysin	3/32	5/62, 2/35
Grimelius		8/133
NSE	3/32	6/62, 13/133
CD56	3/32	6/6 (one case focal)2
bcl-2		2/35
S-100		0/133
p53		3/133, 1/35
CD5		0/35

Differential diagnosis

Metastatic carcinoid, particularly from lung.
Other thymic neuroendocrine tumours
non-neuroendocrine thymic carcinomas
Parathyoid carcinoma
Paraganglioma: negative for cytokeratins

Management

Thymic carcinoids are often not ameneable to complete resection3.

Prognosis

The prognosis is poor, irrespective of grade2, with a median survival of 28 months in one series3. Half of all atypical carcinoids show local invasion or metastases. Distant metastases are common3.

References

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

Moran, C. A. and S. Suster (2000). "Thymic neuroendocrine carcinomas with combined features ranging from well-differentiated (carcinoid) to small cell carcinoma. A clinicopathologic and immunohistochemical study of 11 cases." Am J Clin Pathol 113(3): 345-50.

2Tiffet, O., A. G. Nicholson, et al. (2003). "A clinicopathologic study of 12 neuroendocrine tumors arising in the thymus." Chest 124(1): 141-6.

3de Montpreville, V. T., P. Macchiarini, et al. (1996). "Thymic neuroendocrine carcinoma (carcinoid): a clinicopathologic study of fourteen cases." J Thorac Cardiovasc Surg 111(1): 134-41.

4Warren, J. S. and M. N. Yum (1987). "Carcinoid tumor arising in a treated primary germ cell tumor of the mediastinum." South Med J 80(2): 259-61.

5Histopathology 2004;44:367-374.

This page last revised 13.4.2004.