[Mutation of RAS gene in follicular-differentiated thyroid tumors and its significance]

To investigate the frequency and clinical significance of RAS mutation in thyroid tumors with follicular differentiation. The samples and clinical data of 207 patients with thyroid follicular-differentiated tumors were collected at Shunyi Region Hospital of Beijing from January 2000 to December 2017, including 60 cases of follicular variant of papillary thyroid carcinoma (FVPTC), 42 cases of classical papillary thyroid carcinoma (CPTC), 26 cases of follicular thyroid carcinoma (FTC), 40 cases of follicular adenoma (FTA) and 39 cases of adenomatoid hyperplasia. BRAF V600E mutations were detected using immunohistochemical staining. FVPTC was divided into BRAF-like (BRAF V600E mutant) and RAS-like (without BRAF V600E mutant). Real-time fluorescence quantitative polymerase chain reaction was used to detect the RAS mutation in RAS-like FVPTC, CPTC, FTC, FTA and adenomatoid hyperplasia. The genetic differences in RAS mutation and their correlation with clinicopathological features were analyzed. The average age of patients with benign and malignant tumors in thyroid with follicular differentiation was 53.2 years and 47.7 years, respectively. In these patients, 42 were male and165 were female. Most of the tumors had a maximum diameter of less than 4 cm, and rarely spread to the surrounding tissues of thyroid and were at early stage (stages Ⅰ and Ⅱ). The diameter of tumors in FTC was significantly larger than that in RAS-like FVPTC and CPTC groups (<0.01). Peripheral thyroid invasion was rare in the RAS-like FVPTC, CPTC and FTC groups, but the clinical stage of FTC was more advanced than that of RAS-like FVPTC group (<0.01) or CPTC group (<0.01). The real-time fluorescence quantitative PCR showed that the RAS mutation rate in FTC was the highest (61.5%), significantly higher than that in others (<0.01). The RAS mutation rate in CPTC was the lowest (4.8%), while those in RAS-like FVPTC, FTA and adenomatous hyperplasia were similar (about 15%). The Spearman rank correlation analysis showed that the RAS mutation was not correlated with age, sex or tumor size in benign lesions (FTA and adenomatous hyperplasia), nor was it associated with age, sex, tumor size, lymph node metastasis, spreading of tumors to thyroid and clinical stage in malignant tumors (RAS-like FVPTC, CPTC and FTC). RAS mutation can occur in both benign and malignant thyroid tumors with follicular differentiation, in which the incidence is the highest in FTC. Both morphologic and immunohistochemical changes should be taken into account. The molecular genetics of RAS-like FVPTC is similar to FTA and adenomatous hyperplasia. RAS gene mutation appears not to be a prognostic factor for thyroid diseases.