Nuclear methylation levels in normal and cancerous thyroid cells.

BACKGROUND Most cancers show abnormal DNA methylation and a positive correlation between hypomethylation and tumour progression. PATIENTS AND METHODS In our laboratory the extent of DNA methylation in individual nuclei in normal, cancer and non-cancer thyroid tissue samples was quantified according to a previously described method of computer-assisted semi-quantitative analysis. Cancer and non-cancer samples were obtained from nine patients with different thyroid pathologies (one multinodular goitre and eight carcinomas). Quantitative analysis was performed in two sets of samples, i.e. individual nuclei from touch preparations and from tissue sections. RESULTS In all cancer specimens a statistically significant decrease of heterochromatin methylation was consistently observed. In both sets of samples a direct correlation was consistently observed between the extent of chromatin demethylation and the degree of malignancy. CONCLUSION Our preliminary results suggest that our method of cell-by-cell detection of intranuclear methylation abnormalities may be a useful tool in early identification of thyroid cancer lesions.