Objective   To investigate the value and clinical significance of soluble CD26 (sCD26) in blood in the diagnosis of papillary thyroid carcinoma (PTC).

  Method  A total of 104 PTC patients who had undergone surgery at the Tianjin Medical University General Hospital from January 2013 to December 2017 were collected as the study group. In the study period, surgery had been performed for 25 cases of a benign thyroid lesion, who served as control group. The control also group included 55 cases that had undergone health examination. The fasting blood samples of the PTC group before and after the operation and those of the control group were collected. The sCD26 concentration was determined by ELISA. Clinical pathology features of PTC patients were recorded to analyze the diagnostic value of the sCD26 concentration on PTC and its relationship with clinicopathological features.

  Results  The preoperative sCD26 concentration in PTC patients increased and significantly differed from the control groups. The sCD26 concentration had significantly decreased postoperatively compared to the preoperative value but showed no significant difference from the control group. The sensitivity, specificity, diagnostic accuracy, and optimal diagnostic boundary values for sCD26 distinguishing thyroid carcinoma from benign thyroid lesions were 75.50%, 91.21%, 85.0%, and 545.20 ng/mL, respectively. The results of the chi-square test showed a significant correlation of the high concentration of sCD26 with the tumor size ≥4.0 cm and clinical stage Ⅲ in patients with PTC, but there was no significant correlation with the sex, age, lymph node metastasis, tumor capsule invasion, or preoperative TI-RADS classification.

  Conclusions  The sCD26 concentration has a diagnostic value for PTC and may be an independent predictor of the PTC prognosis.