ObjectiveTo analysis the clinicopathologic features of thyroid tumors with RAS gene mutation. MethodThe clinicopathologic data of thyroid tumor patients, with who underwent surgical treatment or biopsy and were diagnosed pathologically at the Department of Pathology of the Shanghai Sixth People’s Hospital Affiliated to Shanghai Jiao Tong University School of Medicine from January 2021 to June 2023, were collected. ResultsA total of 798 patients with thyroid tumors who met the inclusion criteria were collected, including 747 cases of follicular epithelial tumors and 51 cases of medullary thyroid carcinoma (MTC). Among 798 patients, the RAS gene mutations were detected in 36 cases (4.5%), including 25 (69.4%) patients with NRAS mutations, 8 (22.2%) patients with HRAS mutations, 3 (8.3%) patients with KRAS mutations, and 4 (1.1%) patients accompanied with TERT promoter mutations. Among 36 patients with RAS mutant thyroid tumors, the male to female ratio was 7∶11, with a median age of 48.5 years, with an average tumor diameter of 2 cm. The mutation rate of RAS gene in different histological types of thyroid tumors, from high to low, was highest in the thyroid follicular carcinoma (FTC, 25.9%), followed by differentiated high grade thyroid carcinoma (20.0%), anaplastic thyroid carcinoma (20.0%), noninvasive follicular thyroid neoplasm with papillary like nuclear features (18.2%), follicular variant of papillary thyroid carcinoma (FVPTC, 16.0%), and well-differentiated thyroid tumour of uncertain malignant potential (WT-UMP, 12.8%), the mutation rates of RAS gene in the FTC, FVPTC, and WT-UMP were significantly higher than those of the classical papillary thyroid carcinoma (P<0.001 1), and the mutation rate of RAS gene was the lowest in the classical papillary thyroid carcinoma (1.5%). A total of 35 patients were effectively followed up with an average follow-up of 21.4 months, 6 of whom had cervical lymph node metastasis, 4 patients developed distant metastasis, and 1 patient with anaplastic thyroid carcinoma died. ConclusionsRAS gene mutation can occur in thyroid follicular differentiated tumors and MTC. NRAS mutation is more common. The mutation rate is the highest in FTC, is the lowest in classical papillary thyroid carcinoma. Differential diagnosis combined with tissue morphology and other molecular changes can provide a reference for guiding treatment and evaluating prognosis.