Role of Preablative Stimulated Thyroglobulin in Prediction of Nodal and Distant Metastasis on Iodine Whole-Body Scan

Background: Preablative stimulated thyroglobulin (ps-Tg) is an important investigation in the follow-up of patients with Differentiated thyroid cancer(DTC) after surgery. Levels of ps-Tg > 2-10 ng/ml have been suggested to predict metastasis to cervical and extracervical sites. There is still debate on the need for routine iodine whole-body scan (I-131 WBS) in the management of low-to-intermediate-risk DTC patients. Objective: We analyzed our data of patients with DTC who underwent total thyroidectomy to discuss the predictability of ps-Tg on metastatic disease on the I-131 WBS. Materials and Methods: Retrospective analysis of patient records. Results: One hundred and seventeen patients with DTC (95 papillary thyroid cancer [71 had classic histology, 8 had tall cell variant, 16 had follicular variant] and 22 follicular thyroid cancer [18 minimally invasive, 2 hurtle cell, and 2 widely invasive cancers]) had undergone total thyroidectomy. All these patients underwent ps-Tg assessment and an I-131 WBS. About 65% of them went on to have radioiodine ablation along with a posttherapy I-131 WBS. We divided the cohort into four groups based on their ps-Tg levels: Group 1 (ps-Tg <1), Group 2 (ps-Tg 1-1.9), Group 3 (ps-Tg 2-5), and Group 4 (ps-Tg >5). None of the patients in Group 1, 7% of those combined in Groups 2 and 3 (2 out of 28 patients), and 26% (12 out of 47) of those in Group 4 had either cervical or extracervical metastasis. Those with extracervical metastatic disease to lungs and bones had a mean (standard deviation) ps-Tg value of 436 (130) and median of 500 ng/ml and those with cervical metastatic disease had a mean Tg value of 31 (64) and median 6.6 ng/ml. Conclusions: A ps-Tg value in the absence of anti-Tg antibodies <1 ng/ml reliably excludes metastatic disease in DTC, while a value >5 ng/ml has a 26% risk of having either cervical or extracervical metastasis.