Stimulating thyroglobulin to TSH ratio predict long-term efficacy of I therapy in patients with differentiated thyroid cancer after total thyroidectomy: a retrospective study.

[OBJECTIVE] This study utilized the stimulated thyroglobulin (sTg) to thyroid stimulating hormone (TSH) ratio to predict the long-term efficacy of I therapy in patients with moderate-to-high-risk differentiated thyroid cancer (DTC).

[METHODS] This study retrospectively analyzed 960 DTC patients with a median follow-up time of 30 months (6-92 months). The median age was 44 years. All patients underwent total thyroidectomy, lymph node dissection, and at least one I therapy. Patients were subjected to a final efficacy evaluation according to American Thyroid Association's 2015 guidelines. Patients were grouped according to their TSH levels before the initial I therapy and the final efficacy evaluation, and factors influencing TSH levels and final efficacy were analyzed. Construction of nomograms using independent risk factors affecting long-term outcomes. The cut-offs of sTg and sTg/TSH ratios were calculated for different long-term outcomes. Progression-free survival (PFS) of patients was analyzed by making Kaplan-Meier survival according to the cut-offs of sTg and sTg/TSH ratio.

[RESULTS] TSH (mU/L) levels were more concentrated at 60-90 in females (71.5%) and 30-60 in males (39.0%), while patients with younger age, more lymph node metastases, shorter time interval between surgery and the first I therapy, and lower dose of levothyroxine sodium taken prior to the first I therapy would have higher TSH levels (All P < 0.05).Patients who are male, have primary tumor involvement of the strap muscles, lymph node metastasis, distant metastasis, and higher sTg and sTg/TSH are more likely to have poor long-term outcomes (All P < 0.05).The cut-offs of sTg and sTg/TSH for long-term efficacy were 7.515 and 0.095. STg, sTg/TSH, tumor size, lymph node metastasis, and distant metastasis were shown to be independent risk factors for long-term efficacy. The mean PFSs were longer for patients who had sTg/TSH ≤ 0.095 and/or sTg≤7.515 ug/L.

[CONCLUSIONS] For patients with moderate-to-high-risk DTC, when sTg>7.515 ug/L and/or sTg/TSH > 0.095 before the first I therapy, patients are more likely to have a poor long-term efficacy after full I therapy. This means that this group of patients may require further surgical treatment or targeted drug therapy after I therapy.