Thymic small cell carcinoma

Definition

This is a high grade malignancy, morphologically indistinguishable from the equivalent pulmonary tumour.

Histopathology

The tumour resembling small cell carcinoma of the lung, consisting of small cells with scant cytoplasm. The cells may be polygonal or spindled and show nuclear moulding. The nuclei have finely granular chromatin and inconspicuous cytoplasm. There is a high mitotic rate.

Mixed small cell-epidermoid keratinising carcinoma combines features of small cell carcinoma and epidermoid keratinising thymic carcinoma.

Immunohistochemistry

Cytokeratin	2/24
EMA	2/24
Chromogranin	1/12, 2/24
Synaptophysin	1/12
bcl-2	2/24
NSE	1/12
CD56	1/12
p53	1/24
TTF-1	0/33
CD5	0/24

Differential diagnosis

• Metastatic pulmonary small cell carcinoma.

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

³Cheuk W et al. Immunostaining for thyroid transcription factor-1 and cytokeratin 20 aids in the distinction of small cell carcinoma from Merkel cell carcinoma, but not pulmonary from extrapulmonary small cell carcinoma. Arch Pathol Lab Med 2001;125:228-231. (supplemented by personal communication).

⁴Histopathology 2004;44:367-374.

This page last revised 13.4.2004.

©SMUHT/PW Bishop