Ki67 labelling index correlates with stage and histology but not significantly with prognosis in thymoma

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There have been several cell kinetic studies of thymoma, but the effectiveness of using Ki67 antibody as a tool to measure proliferative activity in this tumour was rarely evaluated. We carried out an immunohistochemical study using this antibody to assess the clinicopathological correlation and the prognostic significance of this technique.

Methods and results:

Ninety-one cases of thymoma were collected. Double immunostaining with Ki67 and cytokeratin KL-1 antibodies was performed on paraffin sections. Ki67 labelling index (LI) was expressed as a percentage of Ki67 immunopositive nuclei by counting at least 1000 epithelial cells. The LIs were correlated with stages, histological subtypes based on both Lattes-Bernatz and Müller-Hermelink-Kirchner classifications, and length of survival. There were statistically significant differences of LIs between stage I and stage III and between stage I and stage IV tumours. Histologically, statistically significant differences were identified between predominantly epithelial thymoma and every other subtype of the Lattes-Bernatz classification and between well-differentiated thymic carcinoma and medullary or mixed thymomas of the Müller-Hermelink-Kirchner classification. Regarding the prognostic implication of Ki67 LI, although there appeared a trend that patients with tumours of higher LIs had slightly worse survival, the difference was not statistically significant in both univariate and multivariate survival analyses.


We have demonstrated the proliferative potential in thymoma is associated with stage and histology. However, its clinical usefulness is limited on account of the overlap of LIs and lack of prognostic significance.

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