Thymic squamous cell carcinoma, epidermoid carcinoma

A thymic tumour showing squamous differentiation, as seen in other organs and lacking an infiltrate of immature T-cells.

Epidemiology

These tumours are rare but are the most common type of thymic carcinoma. The frequency is higher in Asia than in the West.

Clinical features

There may be paraneoplastic polymyositis but not myasthenia gravis, unless the carcinoma has arisen by progression from a thymoma, nor red cell aplasia.

Radiology

Macroscopic appearances

The tumour is not encapsulated and lacks fibrous septa. There is often necrosis or haemorrhage. Invasion of lung, pericardium and major vessels is common. Most tumours are Masaoka stage III or IV at the time of presentation.

Histopathology

These tumours consist of epithelial lobules separated by fibrous bands permeated by inflammatory cells. The squamous cells show intercellular bridges and keratinisation. There is definite cytological atypia. Broad bands of fibrohyaline stroma separate the tumour nests. And lymphocytes are mature and admixed with plasma cells.

Immunohistochemistry

 

Cytokeratin

1/12

 

EMA

1/12

CD5

positive0

CD70

positive0

CD117

positive0

Chromogranin
Synaptophysin
CD56

positive alone or in combination in two-thirds of cases0

   
   

Ultrastructure

Cytogenetics

There are gains of chromosomes 1q, 8, 11, 17q and 18, with losses of 3p, 6, 16q and 17p1.

 

Differential diagnosis

Management

Prognosis

Metastases occur to lymph nodes, bone, lung, liver and brain. The prognosis, along with that of basaloid carcinoma, is better than for other thymic carcinomas.

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 6.1.2006.

©SMUHT/PW Bishop