Thymic low grade metaplastic carcinoma

Synonym

Biphasic thymoma, mixed polygonal and spindle cell type3

These tumours closely resemble thymoma with pseudosarcomatous stroma. However, the epithelial component is described as carcinomatous with variable atypia and mitotic activity. the spindle cell component shows a gradual transition from the epithelial component. Moreover, the spindle cell component is positive for cytokeratins and for EMA. There may be mesenchymal metaplasia with expression of actin, desmin, or neural markers (chromogranin, S-100 or GFAP).

Immunohistochemistry

	epithelial component	spindle cell component
cytokeratins	positive1	positive1
EMA	positive1	positive1
vimentin	positive1	positive1
actin	2/41	2/41
Chromogranin	1/4(minority of cells)1	1/4(minority of cells)1
S-100	1/4(minority of cells)1	1/4(minority of cells)1
GFAP	1/4(minority of cells)1	1/4(minority of cells)1
NSE	1/4(minority of cells)1	1/4(minority of cells)1

Differential diagnosis

Prognosis

One of four patients developed a recurrence.

References

1Yoneda, S., A. Marx, et al. (1999). "Low-grade metaplastic carcinomas of the thymus: biphasic thymic epithelial tumors with mesenchymal metaplasia--an update." Pathol Res Pract 195(8): 555-63.

2Shimosato Y et al. Tumors of the mediastinum. In: Rosai J, Sobin LH, eds. Atlas of Tumor Pathology. 3rd Edn. Armed Forces Institute of Pathology 1997;93-115