[Clinicopathologic study of metaplastic thymoma].
OBJECTIVE
To study the clinicopathologic characteristics of metaplastic thymoma.


METHODS
Resection specimens of 3 cases of metaplastic thymoma were studied by light microscopy, immunohistochemistry and electron microscopy.


RESULTS
All the 3 patients were females and aged 33, 58 and 45 years respectively. Histologically, a biphasic growth pattern, consisting of intimate admixture of epithelial cells and spindle cells, was noted. The epithelial cells showed mild cytologic atypia, sometimes nuclear grooves and pseudonuclear cytoplasmic inclusions. These cells were arranged in nests and anastomosing cords. Mitotic figures were rarely seen. On the other hand, the spindle cells were bland-looking, mitotically inactive and arranged in fascicles. Immunohistochemical study showed that the epithelial cells strongly expressed cytokeratin (AE1/AE3) but not vimentin or CD5. The proliferation index, as demonstrated by Ki-67 immunostaining, was about 3% to 5%. In contrast, the spindle cells were diffusely positive for vimentin and epithelial membrane antigen. Staining for CD5 and CD20 was negative. The background lymphocytes were positive for CD3, but not for TdT and CD99. Ultrastructurally, well-formed desmosomes or hemidesmosomes were identified in the epithelial element. They were not detected within the spindle cells.


CONCLUSIONS
Metaplastic thymoma is a rarely encountered indolent or low-grade thymic tumor and may represent a distinct clinicopathologic entity.
Jin
Mei
M
Department of Pathology, Sir Run Run Shaw Hospital, Zhejiang University, Hangzhou 310016, China. srrshjinmei@163.com
Liu
Biao
B
Wang
Li
L
Xu
Jing-yao
JY
D000328:Adult; D018956:CD5 Antigens / Q000378:metabolism; D003937:Diagnosis, Differential; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007150:Immunohistochemistry; D007633:Keratins / Q000378:metabolism*; D008482:Mediastinum / Q000473:pathology; D008854:Microscopy, Electron; D008875:Middle Aged; D013945:Thymoma / Q000378:metabolism / Q000473:pathology* / Q000648:ultrastructure; D013953:Thymus Neoplasms / Q000378:metabolism / Q000473:pathology* / Q000648:ultrastructure; D014746:Vimentin / Q000378:metabolism
D018956:CD5 Antigens; D014746:Vimentin; D007633:Keratins