Thymic mucoepidermoid carcinoma

Definition

A thymic carcinoma resembling the mucoepidermoid tumour of salivary glands.

Epidemiology

Only about 20 cases have been reported in the English language literature³. There are no reports of an association with type A or B thymoma.

Clinical features

Patients cover a wide age range, with a mean of about 50³. Patients do not have paraneoplastic syndromes³.

Macroscopic appearances

Most tumours show a combination of solid and cystic areas³. Mucoid material fills the cysts³. The solid areas appear nodular with fibrous bands.

Histopathology

The tumour consists of a variable mix of epidermoid and mucinous (goblet) cells, along with intermediate cells. Both the squamous and the mucinous component are well-differentiated. Clear cells and oxyphil cells may also be present³. Mucin is often present within the stroma, accompanied by a lymphoplasmacytic infiltrate, foamy macrophages, cholesterol clefts and fibrosis³. There may be focal calcification or ossification³. Non-neoplastic thymic tissue adjacent to the tumour may show cystic change or mucinous metaplasia³. Grading has been applied as for the equivalent salivary gland tumours³.

Immunohistochemistry

	Cytokeratin	1/12
	CK7+/CK20+	1/53
	CK7-/CK20+	3/53
	EMA	1/12
	CD5	0/12, 0/103
	Chromogranin	0/12
	Synaptophysin	0/12
	p53	0/12
	MUC-2	2/5 (positive in goblet and intermediate cells)3

Ultrastructure

Differential diagnosis

• Tumours with poorly differentiated squamous and mucinous components should be called adenosquamous carcinomas.

Prognosis

See thymic carcinomas

High grade adenosquamous carcinoma is more aggressive than is low grade mucoepidermoid carcinoma.

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.

³ Nonaka, D., D. Klimstra, et al. (2004). "Thymic mucoepidermoid carcinomas: a clinicopathologic study of 10 cases and review of the literature." Am J Surg Pathol 28(11): 1526-31.

This page last revised 6.1.2006.

©SMUHT/PW Bishop