[Immunohistochemical study of 11 epithelial tumors of the thymus or thymomas with anti-keratin antibodies: KL-1].

Eleven cases of epithelial tumours of the thymus or thymoma and two thymuses without tumour were studied, using immunohistochemistry with anti-keratin antibodies (KL-1) which recognise cyto-keratin with a high molecular weight. In the normal thymus, KL-1 positivity seems to be limited to medullary epithelial elements and in particular Hassal's corpuscles. All the epithelial thymic tumours studied showed a net positivity for KL-1 overall in the tumour cells. This result and the demonstration of more or less well differentiated Hassal's corpuscles in these tumours make one think that these epithelial thymic tumours express some characters in relation with a differentiation of medullary type.