Molecular Testing for Mutations in Improving the Fine-Needle Aspiration Diagnosis of Thyroid Nodules

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Abstract
Context: Thyroid nodules are common in adults, but only a small fraction of them are malignant. Fine-needle aspiration (FNA) with cytological evaluation is the most reliable tool for cancer diagnosis in thyroid nodules. However, 10–40% of nodules are diagnosed as indeterminate by cytology, making it difficult to optimally manage these patients. Objective: The aim of this study was to establish the feasibility and role of testing for tumor-specific mutations in improving the FNA diagnosis of thyroid nodules. Design: The prospective study included 470 FNA samples of thyroid nodules from 328 patients. At the time of aspiration, a small portion of the material was collected and tested for BRAF, RAS, RET/PTC, and PAX8/PPARγ mutations. The mutational status was correlated with cytology and either surgical pathology diagnosis or follow-up (mean, 34 months). Results: A sufficient amount of nucleic acids were isolated in 98% of samples. Thirty-two mutations were found, including 18 BRAF, eight RAS, five RET/PTC, and one PAX8/PPARγ. The presence of any mutation was a strong indicator of cancer because 31 (97%) of mutation-positive nodules had a malignant diagnosis after surgery. A combination of cytology and molecular testing showed significant improvement in the diagnostic accuracy and allowed better prediction of malignancy in the nodules with indeterminate cytology. Conclusions: These results indicate that molecular testing of thyroid nodules for a panel of mutations can be effectively performed in a clinical setting. It enhances the accuracy of FNA cytology and is of particular value for thyroid nodules with indeterminate cytology.