3055 Background: Ultrasound and ultrasound-guided fine needle aspiration (US-FNA) are the first choice for judging benign and malignant thyroid nodules. This study will report on the differences of US-FNA BSRTC class, postoperative pathology and mutation landscape of thyroid nodules between China and other countries. Methods: We conducted a prospective study containing 383 FNA samples of thyroid nodules. For most of these FNA samples, genomic DNA and RNA were extracted and sequenced with FSZ-Thyroid NGS Panel V1, and postoperative pathology were followed up. Moreover, we also compared results of this study with those of West China Hospital in China, Yamashita Thyroid Hospital in Japan, and Cleveland Clinic in the United States. Results: Among the 383 FNA samples, the proportions of BSRTC class I to VI were 10.7%, 6.3%, 18.8%, 3.7%, 12.3%, and 48.3% respectively. Compared with study in other countries, the proportion of class II was significantly lower than that in Japan and the United States. Meanwhile, the proportion of class V and VI were significantly higher than the above two countries. Subsequently, 232 thyroid nodules were surgically removed. Postoperative pathology showed that the proportion of malignant tumors (85.3%) was also significantly higher than reported in Japan and the United States. But compared with other studies in China, there was no significant difference. Most of the malignant tumors were papillary thyroid cancer (PTC, 96%), accompanied with 2 follicular thyroid cancer (FTC), 3 medullary cancer (MTC) and 3 anaplastic thyroid cancer (ATC). Compared with study in the United States, the proportion of PTC and FTC were elevated (96% vs. 85.3%) and reduced (1% vs. 9.3%) respectively. At last, we also analysis the mutation landscape of 180 malignant tumors. Compared with TCGA study, the frequency of BRAF V600E in PTC in our study was significantly higher than that of TCGA (73.3% vs. 58%), and the frequency of RAS mutation was significantly lower (1.2% vs. 12.6%). And compared with an institutional experience of ThyroSeq v3 for Bethesda III and IV at the University of Pittsburgh Medical Center, the frequency of BRAF V600E and RAS mutation in Bethesda III-IV malignant tumors was also significantly higher (45.8% vs. 1.4%) and lower (8.3% vs. 47.1%). Conclusions: There were significant differences in BSRTC class and postoperative pathology between China and other countries, such as Japan and the United States. The possible reasons included that the indications for FNA in China were different. For example, most of patients who underwent FNA in this study had suspicious clinical/ultrasound features. So the proportion of BSRTC class V and VI as well as the malignant rate were elevated. On the other hand, more BRAF V600E and less RAS mutations were detected in malignant tumors in this study which might result from racial differentiation and discrepancy in proportion of PTC and FTC.
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