Immunophenotype of Thymic Epithelial Tumors According to the New World Health Organization Classification

ABSTRACT

BACKGROUND: To identify the expression patterns and usefulness of various antibodies in making diagnoses and predicting prognoses, an immunohistochemical study was performed on thymic epithelial tumors (TETs). METHODS: Forty-two cases of TETs were reclassified according to the new World Health Organization (WHO) classifications. CD3, CD5, CD79a, CD99, pan-, high- and low-molecular weight cytokeratins, EMA, vimentin, MIB-1 (Ki67) and p53 immunostaining were carried out. RESULTS: There were two, twelve, eight, two, thirteen and one case for type A, AB, B1, B2, B3 and C, respectively. Combined B1/B2 and B2/B3 were 2 cases each. Fourteen cases (33.3%) had myasthenia gravis. CD99 was immunoreactive mainly in cortically derived lymphocytes, while CD3 and CD5 were immunoreactive in medullary-derived lymphocytes. CD5 immunoreactivity was negative in all thymic epithelial cells, except for one case of type B3. MIB-1 indices were highly expressed in cortical lymphocytes and some thymic epithelial cells, but did not show any correlation with grades. p53 in thymic epithelial cells was expressed in 6 (46%) out of 13 cases of type B3 and one case of type C, and it was negative in all other subtypes. CONCLUSIONS: Only p53 was helpful for predicting high grades (B3 and C) (P<0.05). By MIB-1 indices, we could tell how many cortical immature lymphocytes were occupied in TETs, however, grading could not be achieved.