Objective  To investigate the risk factors for distant metastasis in patients with differentiated thyroid cancer (DTC), construct a nomogram prediction model for distant metastasis, and assess its predictive value.

Methods  The clinical and histopathological examination data of 655 patients with DTC admitted to the First Hospital of Shanxi Medical University from December 2018 to December 2021 were retrospectively analyzed. The patients included 221 males and 434 females aged (44.4±11.5) years with an age range of 10–77 years. The risk factors for distant metastasis in patients with DTC were determined through univariate analysis, and their optimal cut-off values were established through receiver operating characteristic (ROC) curve analysis. Multivariate Logistic regression analysis was employed to identify independent risk factors for distant metastasis in patients with DTC, and a nomogram prediction model was developed. The discrimination ability, calibration, and clinical net benefit of the model were assessed on the basis of ROC curves, calibration curves, and clinical decision curve analysis (DCA).

Results  Univariate analysis indicated that gender, age, pathological type, maximum tumor diameter, vascular tumor thrombus, capsule or extrathyroidal extension, lateral cervical lymph node metastasis, lateral cervical lymph node metastasis combined with central lymph node metastasis, metastatic lymph node number, the interval between the first ¹³¹I treatment and operation, and stimulated thyroglobulin (sTg) level before ¹³¹I treatment were risk factors for the distant metastasis of DTC (χ²=4.150–215.57, all P<0.05). The optimal cut-off values for age, maximum tumor diameter, metastatic lymph node number, the interval between the first ¹³¹I treatment and operation, and sTg level before ¹³¹I treatment for predicting distant metastasis were 55 years old (area under the curve (AUC)=0.548, 95%CI: 0.452–0.643), 2 cm (AUC=0.740, 95%CI: 0.663–0.818), 6 (AUC=0.684, 95%CI: 0.605–0.764), 3 months (AUC=0.625, 95%CI: 0.548–0.702), and 19.43 ng/ml (AUC=0.927, 95%CI: 0.886–0.967), respectively. Multivariate Logistic regression analysis revealed that age ≥55 years old, maximum tumor diameter ≥2 cm, metastatic lymph node number ≥6, and sTg level before ¹³¹I treatment ≥19.43 ng/ml were independent risk factors for the distant metastasis of DTC (OR=3.427–34.239, all P<0.05). The constructed nomogram prediction model had good predictive performance, including good discrimination ability (AUC=0.920, 95%CI: 0.877–0.963, P<0.05) and calibration (mean absolute error=0.007). The clinical DCA results showed that the model had good clinical net benefit.

Conclusions  Age ≥55 years old, maximum tumor diameter ≥2 cm, metastatic lymph node number ≥6, and sTg level before ¹³¹I treatment ≥19.43 ng/ml are independent risk factors for predicting the distant metastasis of DTC. The nomogram prediction model established on the basis of these factors has good efficacy and can be used as a tool for the clinical personalized assessment of the risk of distant metastasis in patients with DTC before ¹³¹I treatment.