Ki-67 positive fractions in benign and malignant thyroid tumours: application of flow cytometry

We investigated the DNA ploidy pattern, cell cycle and the percentage of Ki-67 positive fractions in fresh surgical material from 17 benign and 33 malignant thyroid tumours using flow cytometry. DNA aneuploidy was not seen at all in benign tumours, but was seen in 3 out of 33 malignant tumours, suggesting that detection of DNA aneuploidy indicates malignancy, although the detection sensitivity was low. Regarding the cell cycle, there was no difference in the percentage of S-phase fractions (SPF) or G2 plus M phase fractions (G2M) between benign and malignant tumours. However, the percentage of Ki-67 positive fractions in malignant tumours (39.9 +/- 3.9%) was significantly higher than that in benign tumours (9.4 +/- 2.1%), indicating that malignant thyroid tumours contained a large population of G phase cells. When a cut-off value of 20%, was used for Ki-67 positive fractions, sensitivity was 82%, specificity was 88% and accuracy was 84% for the diagnosis of malignant tumours. Although this study was carried out on surgically derived materials, it is possible that flow cytometric analysis of fine needle aspiration-derived materials may have a place in preoperative histopathological assessment of thyroid tumours.