Diagnostic utility of genetic testing for thyroid tumor

Abstract

Background: In the 2015 American Thyroid Association Management Guidelines and The Bethesda System for Reporting Thyroid Cytopathology (2nd edition), a molecular biological search was indicated for certain clinical responses after cytological diagnosis. Genetic testing of thyroid tumor patients is considered to improve diagnostic accuracy and confirm the preoperative diagnosis. In this study, we examined the utility of genetic testing for the diagnosis of thyroid tumors. Methods: Thyroid tumors surgically resected from 40 patients and histopathologically diagnosed in our hospital between 2013 and 2017 were examined. The tumors were obtained from 15 patients with papillary carcinoma (conventional type), 15 patients with follicular carcinoma (excluding oxyphilic cell type), five patients with follicular adenoma (excluding oxyphilic cell type), and five patients with adenomatous goiter. By using DNA and total RNA extracted from FFPE sections, we searched for BRAF mutations, RAS mutations, RET rearrangements, and PAX8/PPARg rearrangements. Results: Genetic abnormalities (BRAF mutation V600E: 12 patients; RET/PTC1 rearrangement: 1 patient) were detected in 13 out of 15 papillary carcinoma patients (86.7%). In follicular carcinoma patients, 10 out of 15 revealed genetic abnormalities (NRAS mutation Q61R: 3 patients; Q61K: 2 patients; KRAS mutation Q61R: 2 patients; HRAS mutation Q61R: 2 patients; PAX8/PPARg rearrangement: 1 patient) (66.7%). No genetic abnormality was detected in patients with follicular adenoma and adenomatous goiter. Conclusions: In thyroid tumors, BRAF mutations, RAS mutations, RET rearrangements, and PAX8/PPARg rearrangements are highly specific to the histopathological type. The genetic testing for thyroid tumors will provide useful information for morphologic diagnosis of difficult cases and contribute to the improvement in diagnostic accuracy.