Argyrophilic nucleolar organizer regions in cells of thymoma and thymic carcinoma - Correlation with DNA ploidy and clinicopathologic characteristics

Study objectives: To evaluate the usefulness of argyrophilic nucleolar orga nizer region (AgNOR) counting and flow cytometric DNA analysis in the diffe rential diagnosis of thymoma and thymic carcinoma, as well as in the differ ences among various stages and histologic subtypes of these tumors. Design and interventions: Paraffin-embedded blocks of 64 thymic epithelial tumors (20 noninvasive thymomas, 34 invasive thymomas, and 10 thymic carcin omas) were studied by AgNOR counting and flow cytometric DNA analysis. The thymomas were histologically classified as medullary, cortical, or mixed su btype, Measurements and results: Invasive thymomas had more AgNORs (+/- SD) than n oninvasive thymomas (7.93 + 2.90 vs 5.97 +/- 1.77; p < 0.01). The number of AgNORs of thymoma increased progressively with advances in stage (p < 0.01 ), Cortical thymomas had the highest number of AgNORs among the three subty pes (p < 0.05), Patients with thymoma who presented with myasthenia gravis also had a higher number of AgNORs (8.30 +/- 3.12 vs 6.50 +/- 2.03; p < 0.0 1). The AgNOR number did not correlate with the DNA ploidy of all specimens . Conclusions: AgNOR counting is useful in differentiating between invasive a nd noninvasive thymomas, and in predicting the stage of thymomas, A greater number of AgNORs was observed in patients with cortical thymoma and in tho se who presented with myasthenia gravis.