BACKGROUND

Cancer-specific molecular markers are needed to supplement the cytopathological assessment of thyroid tumors, because a majority of patients with cytologically indeterminate nodules currently undergo thyroidectomy without a definitive diagnosis.

OBJECTIVE

The aim of this study was the quantitative assessment of promoter hypermethylation and its relation to the BRAF mutation in thyroid tumors.

METHODS

Quantitative hypermethylation of Rassf1A, TSHR, RAR-beta2, DAPK, S100, p16, CDH1, CALCA, TIMP3, TGF-beta, and GSTpi was tested on a cohort of 82 benign and malignant thyroid tumors and five thyroid cancer cell lines.

METHODS

The study was conducted at a tertiary research hospital.

METHODS

Patients underwent surgical resection for a thyroid tumor from 2000 to 2003 at our institution.

METHODS

There were no interventions.

METHODS

Final surgical pathology diagnosis was the main outcome measure.

RESULTS

Thyroid tumors showed hypermethylation for the following markers: Rassf1A, TSHR, RAR-beta2, DAPK, CDH1, TIMP3, and TGF-beta. A trend toward multiple hypermethylation was evident in cancer tissues, with hypermethylation of two or more markers detectable in 25% of hyperplasias, 38% of adenomas, 48% of thyroid cancers, and 100% of cell lines. A rank correlation analysis of marker hypermethylation suggests that a subset of these markers is epigenetically modified in concert, which may reflect an organ-specific regulation process. Furthermore, a positive correlation was found between the BRAF mutation and RAR-beta2, and a negative correlation was found between the BRAF mutation and Rassf1A.

CONCLUSIONS

Methylation-induced gene silencing appears to affect multiple genes in thyroid tissue and increases with cancer progression. Additional markers with better discriminatory power between benign and malignant samples are needed for the diagnostic assessment of cytologically indeterminate thyroid nodules.