Risk factor for Persistent Metastatic Neck Lymph Nodes after I-131 Ablation Therapy in Papillary Thyroid Cancer

Objectives I-131 ablation after thyroidectomy can find and eradicate hidden residual lesions in differentiated thyroid cancer, however the residual lesions can persist after the ablation. Aim of the study is to investigate risk factors for persistent metastatic cervical lymph node (LN)s after first I-131 ablation therapy in papillary thyroid cancer(PTC).

Methods Among 1412 PTC patients who received I-131 ablation, 109 (87 Women, 22 Men; average age: 48±12 years) patients who revealed unsuspected metastatic cervical LNs on postablation whole body scan or SPECT (PaSCAN) and also had appropriate clinical follow-up data were enrolled in this study. Each patient was followed-up at least 6 months after ablation (median: 23 month). Persistent disease was diagnosed by pathologically or clinico-radiologically. Clinical, pathologic, and biochemical factors and imaging findings were reviewed, and their relationships to persistent disease were analyzed.

Results 267 patients (19.1%) had metastatic LNs on PaSCAN, and 158 patients were excluded from the study due to loss of follow-up and, finally, 109 patients was analyzed for the study. 101 (92.7%) among 109 patients (eradication group) revealed no evidence of disease during follow-up study without any further treatment and 8 patients (7.3%) (persistence group) revealed persistent disease. Although there were no significant difference of clinical and pathologic risk factors between persistence and eradication groups, however, persistence group showed high preablation Tg (34.89 ± 59.24 vs. 6.05 ± 20.32 ng/ml, p = 0.002) and high number of metastatic LN on PaSCAN (2.12 ± 0.64 vs. 1.57 ± 0.74, p = 0.0434). Preablation Tg (cut off=2.6, HR: 16.8, p = 0.0108) and number of metastatic LN on PaSCAN (cut off = 1, HR: 9.3, p = 0.0462) were predictors for the persistent disease.

Conclusions Although, incidence of hidden cervical metastatic LNs was relatively high in thyroidectomized PTC patients, majority of patients with the metastasis was eradicated by I-131 ablation. However, careful follow-up for persistent disease might be needed in cases with high preablation Tg level or multiple LNs metastases.