Second radioiodine treatment hardly benefits TT-DTC patients with radioiodine-negative metastases on initial post-therapeutic whole-body scans

The effect of second 131I treatment (RT) in totally thyroidectomized differentiated thyroid cancer (TT-DTC) patients with true-positive thyroid beds and false-negative metastasis (TB+/M-) on initial post-therapeutic whole-body scan (Rx-WBS) remains unknown.TT-DTC patients with TB+/M- on initial Rx-WBS receiving and not receiving second RT were categorized into group A and group B, respectively, while patients with 131I-avid metastasis receiving second RT were referred to as group C. Biochemical remission (BR) was defined as a decrease of ≥25.0% in thyrotropin-suppressed thyroglobulin (Tgon) level, while the structural response (SR) was determined by the change in the size of the largest lesion.In total, 145 patients were eligible. In group A, the median Tgon measured 3.3 ng/mL before and 3.0 ng/mL at 4 months after second RT (P=0.307), yielding a decrease in the median Tgon (∆Tgon%) of 13.3%, a BR rate of 36%, and an insignificant SR, which were comparable to those in group B. In group C, however, a median ∆Tgon% of 37.8% and a BR rate of 64% were obtained, which were significantly higher than those in group A (P=0.038 and 0.022, respectively), with SR distributions similar to those in group A. In addition, 131I uptake in the neck was not statistically associated with the detection of metastasis on initial Rx-WBS.This controlled study demonstrated a subtle response to second RT in TT-DTC patients with TB+/M- on initial Rx-WBS, representing a meaningful advancement in avoiding ineffective repeated RT.