Papillary carcinoma of the thymus

Epidemiology

This is a rare primary carcinoma of the thymus, only five cases having been reported. It occurs in the elderly.

Clinical features

Paraneoplastic syndromes have not been reported.

Macroscopic appearance

The tumour appears encapsulated but is often adherent to lung, pleura or pericardium and may show pleural implants. There may be cysts.

Histopathology

The tumour has a tubulopapillary architecture. Matsuno et al¹ described four cases of papillary carcinoma arising in the thymus. Three showed low-grade atypia and were associated with spindle cell- type thymoma. The fourth case showed high-grade atypia and had no evidence of an association with thymoma. Two of three low-grade cases invaded the lung and showed extensive lymphatic permeation. Cyst formation was seen in one case. The histological similarities and the intimate association with Type A (spindle cell) thymoma indicate that papillary thymic carcinoma may arise from the papillotubular formations sometimes seen in the former tumour. Extensive lymphatic permeation may be seen. There may be psammoma body formation². Immature T-cells are absent.

Immunohistochemistry

CEA	4/41
Leu-M1	4/41
Ber-EP4	4/41
calretinin	2/41
CD5	4/41
CD20	negative0
Calretinin	negative0
thyroglobulin	0/41
pulmonary surfactant apoprotein	0/41

Differential diagnosis

Papillary thymic carcinoma should be considered in the differential diagnosis of anterior mediastinal tumors. Conceivably, it may be the source of some metastatic papillary carcinomas, with or without psammoma bodies, in cervical lymph nodes, in which no tumor is found in the thyroid gland.

• Papillary carcinoma of the thyroid.

• Mesothelioma.

• Germ cell tumour.

• Adenocarcinoma of foregut cyst.

Prognosis

Currently not known.

References

⁰ Tumours of the Lung, Pleura, Thymus and Heart. WHO Classification of Tumours. IARC Press 2004.

¹ Matsuno, Y., Morozumi, N., Hirohashi, S., Shimosato, Y., Rosai, J. Papillary carcinoma of the thymus: report of four cases of a new microscopic type of thymic carcinoma. Am J Surg Pathol 1998;22:873-80.

² J Rosai et al. Histological typing of tumours of the thymus. WHO International histological classification of tumours. Springer-Verlag, second edition, 1999.

This page last revised 14.1.2006.

©SMUHT/PW Bishop