Effect of Lymph Node Metastasis on Change of Positive Thyroglobulin Antibody in Differentiated Thyroid Carcinoma after Initial Treatment.

Objective To investigate the influence of lymph node metastasis on the change of positive thyroglobulin antibody(TgAb)in differentiated thyroid carcinoma after initial treatment.Methods We retrospectively analyzed the clinical data of 98 differentiated thyroid carcinoma patients with positive TgAb(≥115 IU/ml)before radioiodine(RAI)therapy.All of whom underwent total or near total thyroidectomy,neck lymph node dissection,and subsequent RAI therapy.Patients were divided into negative group(n=83)and non-negative group(n=15)according to the disappearance of positive TgAb or not after a mean follow-up of 21.0 months.Analysis of variance,χ test,and Mann-Whitney rank-sum test were applied to compare the basic clinical features including number of metastatic lymph nodes,lymph node metastasis rate and node stage,and dose of RAI ablation.The receiver operating characteristic curves were employed to evaluate the predictive values of TgAb levels(negative or positive)and optimal cut-off points.Multivariate analyses were further performed to explore the independent indicators for persistent positive TgAb. Results Compared with the negative group,the proportions of N1a and N1b in the non-negative group were significantly higher,with no N0 in the non-negative group(Fisher's Exact Test,P=0.032).The median metastatic lymph node rate was also significantly higher in the non-negative group(Mann-Whitney U=-3.498,P=0.000).The cut-off value for metastatic lymph node rate to predicting disappearance of positive TgAb was 24%,and its sensitivity was 71.4%.The multivariate analysis showed that only lymph node stage(OR=3.183,P=0.038)was the independent indicator for persistent positive TgAb. Conclusions Lymph node stage was an independent indicator for the disappearance of positive TgAb.A metastatic lymph node rate of higher than 24% may be predictive for the disappearance of positive TgAb.