Objective  To continuously evaluate the response of differentiated thyroid cancer (DTC) after radioiodine therapy, and to analyze influencing factors for excellent response.

  Methods  Data of 237 patients with non-distant metastatic DTC treated in Peking Union Medical College Hospital were retrospectively analyzed, and the changes in response were evaluated (excellent response, ER; biochemical incomplete response, BIR; and structure incomplete response, SIR) 2 years after receiving the ¹³¹I therapy. The responses of different recurrence-risk stratification and TNM stages were contrasted, and the influencing factors to ER were analyzed by multiplefactor analysis.

  Results  The percentage of the responses obtained 3 months and 2 years after ¹³¹I therapy were (3 months/2 years) as follows: 54.9%/73.0%, 33.3%/18.1%, 11.8%/6.0%, and 0/3.4%. Of the initial IR patients, 45.6% were observed to transfer into ER and 28.6% of the BIR patients are confirmed cervical recurrence by pathology. Recurrence-risk stratification and ER rate were negatively correlated (r=0.973, P=0.147); however, TNM stage and response showed no evident correlation. The size of tumor and the number of lymph node metastasis were the main influencing factors in obtaining ER (P=0.008, 0.007, respectivtly).

  Conclusion  The rate of ER in non-metastasis DTC patients increased gradually after receiving ¹³¹I therapy. Approximately half of initial IR patients reached ER two years after treatment, and the patients with small diameter of tumor and less lymph node invasion tend to obtain ER.