Abstract: Objective　To investigate the value of microRNA-155 (miR-155) combined with ultrasound in the diagnosis of lymph node metastasis in differentiated thyroid carcinoma. Methods　A total of 112 patients with differentiated thyroid cancer who were treated in our hospital were selected as thyroid cancer group, and 30 patients with nodular goiter in the same period were selected as benign control group. Real time quantitative PCR (qPCR) was used to detect the relative expression of miR-155 in serum and tissue in the two groups of patients. The relationship between the expression of miR-155 in serum and tissue of patients with differentiated thyroid cancer and clinical pathological parameters was analyzed. Receiver operating characteristic (ROC) curve was used to analyze the diagnostic value of preoperative ultrasound and serum miR-155 for lymph node metastasis of differentiated thyroid cancer. Results　The relative expressions of miR-155 in serum and tissue were significantly higher in thyroid cancer group than those in benign control group (P＜0.01). The relative expression levels of miR-155 in serum and tissue were significantly higher in patients with lymph node metastasis, tumor size＞2 cm and TNM stage Ⅲ+Ⅳ than those in patients without lymph node metastasis, tumor size≤ 2 cm and TNM stageⅠ+Ⅱ (all P＜0.05). ROC results showed that ultrasound and serum miR-155 had certain diagnostic value for lymph node metastasis of differentiated thyroid carcinoma. The area under the curve was 0.839 (95%CI: 0.760-0.919) and 0.837 (95%CI: 0.763-0.912), respectively. But the missed diagnosis rate and misdiagnosis rate were more than 10%. The combined application of the two methods could further improve the diagnostic value of lymph node metastasis of differentiated thyroid cancer, the area under the curve was 0.912 (95%CI: 0.851-0.973), and the missed diagnosis rate and misdiagnosis rate were also reduced to less than 10%. Conclusion　The serum miR-155 combined with ultrasound has high diagnostic value for the lymph node metastasis of differentiated thyroid carcinoma, which has certain clinical application value.

Key words: thyroid neoplasms, lymphatic metastasis, ultrasonography, microRNAs, ROC curve, differentiated thyroid carcinoma, microRNA-155