Thymic carcinosarcoma associated with a spindle cell thymoma: an immunohistochemical study.

A case of thymic carcinosarcoma associated with a spindle cell thymoma in a 71-year-old woman is reported. Histological and immunohistochemical studies of the carcinosarcoma showed two quite different components: the sarcomatous component included cells with myoid differentiation which stained for desmin and muscle specific actin, and some isolated cells which stained positively for low molecular weight cytokeratin, while the carcinomatous component, which formed less than 10% of the tumour, showed an epithelial phenotype, being positive for low and high molecular weight cytokeratin and epithelial membrane antigen. The thymoma cells showed epithelial markers, and a few cells were also positive for desmin and muscle specific actin. The rarity of this tumour and its possible histogenesis are discussed.