Endocrine Abstracts

Aim: Stimulated thyroglobulin (sTg), measured at radioiodine remnant-ablation (RRA) in patients with differentiated thyroid cancer(DTC), is an important predictive factor of persistent disease. However, Tg produced by normal thyroid cells may also contribute to the sTg value.

We aimed to study the relationship between sTg-level in RRA and the thyroid remnant size (TRs), using post-therapy whole-body scan (131I-ptWBS), at different TSH stimulation method.

Materials and methods: We review DTC cases referred for RRA, either prepared with recombinant-human TSH (rhTSH) or after 4-weeks levothyroxine withdrawal (hipo). Anti-thyroglobulin antibodies (TgAb) and sTg were measured. Patients with positive TgAb, 131I-uptake outside the thyroid bed and suspected to have persistent disease on the first 6–12 months were excluded. Four hundred patients (331 women, 69 men;mean age sd:49.8 14.1 years-old) were selected. TRs was assessed by 131I-ptWBS, using a fixed circular region-of-interest (ROI) placed in thyroid bed. The geometric mean (GM) of the total counts (cts) in the ROI was calculated, corrected for the thigh background and normalized for the treatment activity (nGM). Based on nGM, remnants were classified into small(S)-nGM<=10cts/MBq; medium(M)-10cts/MBq<nGM<=50cts/MBq and large (L)-nGM>50cts/MBq. Spearman’s rank correlation coefficient was used to test the association between TRs and the sTg normalized for TSH(nTg). SPSS version-23 was used for statistical analyses.

Results: A moderate positive correlation between nGM and nTg was found in rhTSH and hipo patients (rs=0.55, P<0.001 and rs=0.59, P<0.03 respectively). For the all population we found a strong positive correlation(rs=0.61,P<0.002). A positive moderate correlation was found in group-S and L (rs=0.58, P<0.01; rs=0.42, P<0.034 respectively); a weak positive correlation in group-M (rs=0.08, P<0.19).

Conclusion: Radioiodine-scintigraphy and sTg are important tools to evaluate the functional status of both normal and neoplasic thyroid tissue. Our results suggest that TRs and sTg values are correlated, in the absence of clinical/imagiological disease, regardless the method of TSH stimulation. We hypothesize that sTg values are a better predictor of TRs in patients with less TRs.