Clinical Risk Factor for Detected Distant Metastasis and Anaplastic Transformation After Reoperation in Recurrent/Persistent Differentiated Thyroid Cancer: A Retrospective Cohort Study

Objectives Research on detected distant metastasis or anaplastic transformation in recurrent/persistent differentiated thyroid cancer is limited. We analyzed the clinical factors associated with detected distant metastasis or anaplastic transformation following reoperation for differentiated thyroid cancer. Methods This retrospective review included 336 patients who underwent reoperation for differentiated thyroid cancer with detection of distant metastasis or anaplastic transformation following reoperation. The hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated. Results Distant metastasis was detected in 45 patients (45/336, 13.4%) after reoperation. The risk of distant metastasis was higher for patients of male sex (adjusted HR: 2.373; 95% CI: 1.133–4.973), age ≥ 55 (adjusted HR: 4.991; 95% CI: 2.451–10.165), initial T3‐4 stage (adjusted HR: 2.347; 95% CI: 1.035–5.321), in‐field recurrence (adjusted HR: 3.267; 95% CI: 1.489–7.168), and those who had undergone ≥ 3 reoperations (adjusted HR: 3.378; 95% CI: 1.248–9.174). Anaplastic transformation was detected in 7 patients (7/336, 2.1%) after reoperation. The risk of anaplastic transformation was higher for patients with an age ≥ 55 (adjusted HR: 6.811; 95% CI: 1.300–35.676) and those who had undergone ≥ 3 reoperations (adjusted HR: 5.672; 95% CI: 1.139–28.236). Conclusion In recurrent/persistent differentiated thyroid cancer, distant metastasis or anaplastic transformation following reoperation is not insignificant. There may be increased risk of distant metastasis or anaplastic transformation with multiple reoperations in patients who are men, aged ≥ 55, or at the initial T3–T4 stage. Level of Evidence 4.