Change of pre-ablative thyroid-stimulating hormone after thyroid hormone withdrawal and its response to 131I therapy in patients with low to intermediate risk differentiated thyroid cancer

Abstract

Objective To investigate the relationship between the change of pre-ablative TSH after thyroid hormone withdrawal(THW) and the response of subsequent 131I therapy in patients with low to intermediate risk DTC after total or near total thyroidectomy. Methods A total of 120 DTC patients (38 males, 82 females, age (40.8±10.9) years) were enrolled in this retrospective study. Serial TSH levels determined on the day of THW and on the day of receiving 131I ablative therapy were monitored, which were marked as TSH1 and TSH2 accordingly. The THW duration (t) was recorded, the change of TSH was defined as ΔTSH and the change rate of TSH was calculated (V=ΔTSH/t). The responses to 131I therapy were classified as excellent response(ER), indeterminate response (IDR), biochemical incomplete response (BIR) and structural incomplete response (SIR) according to ATA guideline. According to the TSH2 (mU/L) levels, patients were divided into G1 group (30≤TSH2 5.0) , and their responses to 131I ablation were compared. Patients were classified into R1 group (including ER and IDR) and R2 group (including BIR and SIR), the differences of clinical and pathological features, 131I doses between the two groups were explored. Furthermore, logistic regression was performed to identify factors associated with BIR and SIR. Results Patients with male gender (χ2=11.863), younger age(F=4.975), and faster TSH change rate (H=44.911) and lower thyroid residue (H=18.159) achieved a higher value of TSH2 (all P 0.05). TSH2 level(OR=0.835) and pre-ablative Tg level (OR=1.196) were independent factors in predicting BIR and SIR (both P<0.05). Conclusions The changing rate of TSH before 131I ablation may not be associated with the response to 131I therapy in patient with low to intermediate risk DTC, while the level of TSH2 does. Patients with TSH2 ranging from 90 to 120 mU/L could be of help in achieving a better clinical response. Key words: Thyroid neoplasms; Thyrotropin; Radiotherapy; Iodine radioisotopes; Treatment outcome