Carcinoma showing thymus-like differentiation of the thyroid, CASTLE

Definition

CASTLE is a rare tumour of the thyroid, architecturally resembling thymic squamous cell or lymphoepithelioma-like carcinomas. They may arise from the solid cell nests to be found in the posterior aspect of the thyroid gland.

Epidemiology

CASTLE most commonly occurs in the fifth decade of life. There is a female predominance.

Clinical features

Patients present with a painless mass or with hoarseness. About one third of patients present with nodal metastases.

Histopathology

The tumour is lobulated, composed of islands of squamoid, spindled or syncytial cells. The cells have pale cytoplasm and vesicular nuclei.

Immunohistochemistry

	CD5	7/71
	p63	7/7(diffuse in 6 cases, focal in 1 case)1
	CEA	5/51
	34bE12	5/51
	TTF-1	negative
	thyroglobulin	negative
	calcitonin	negative

Differential diagnosis

Thyroid squamous cell carcinoma: negative for CD5.

Prognosis

This is an indolent tumour with a good prognosis.

References

1 Reimann JD, Dorfman DM, Nose V. Carcinoma Showing Thymus-like Differentiation of the Thyroid (CASTLE): A Comparative Study: Evidence of Thymic Differentiation and Solid Cell Nest Origin. Am J Surg Pathol 2006; 30:994-1001

This page last revised 19.8.2006.