Definition of the Response to Initial Therapy with Radioiodine in Patients with Differentiated Thyroid Carcinoma: Basal or Stimulated Thyroglobulin?

Abstract

Basal thyroglobulin (b-Tg) measured with second-generation assay or stimulated Tg (s-Tg) can be used to define the response to therapy of differentiated thyroid carcinoma. However, they do not always define the same category and guidelines do not establish “if” or “when” s-Tg needs to be obtained. We studied 304 patients without clinically apparent disease or disease detected by neck ultrasonography and without anti-Tg antibodies 9–12 months after therapy. Based on b-Tg, 196 patients had an excellent response and 108 had an indeterminate response. Based on s-Tg, a change in category occurred in 10.2% of the patients with an initial excellent response (all to indeterminate response) and in half the patients with an initial indeterminate response (44.4% to excellent response and 5.5% to biochemical incomplete response). One case of recurrence was observed among patients with an initial excellent response but whose response changed to indeterminate after s-Tg, while no disease was detected among those who remained in the initial category; however, this difference was not significant. In patients with an initial indeterminate response, no recurrence was detected among those whose response changed to excellent after s-Tg, while 11.1 and 33.3% of those who remained in the initial category or whose response changed to biochemical incomplete, respectively, had structural disease. This study suggest that, in low- or intermediate-risk patients, s-Tg better defines the response to therapy with 131I when it is classified as indeterminate based on b-Tg using second-generation assay. However, s-Tg is not necessary when b-Tg defines the response as excellent.

Thyroglobulin Antibodies as a Prognostic Factor in Papillary Thyroid Carcinoma Patients with Indeterminate Response After Initial Therapy

“…The role of basal and/or stimulated Tg in evaluation of therapy in patients with indeterminate response is not well established. Based on sTg, a change in category occurred in half the patients with an initial indeterminate response, 44.4 % to excellent response and 5.5 % to biochemical incomplete response and others remained in same category [15]. Interestingly, some studies have demonstrated that if sTg is done 5 years after the initial treatment, the vast majority of responses originally classified as indeterminate (up to 98 %) can be reclassified as excellent response [16].…”

Is Stimulated Thyroglobulin Before Radioiodine Therapy a Useful Tool in Predicting Response to Initial Therapy in Patients with Differentiated Thyroid Carcinoma?

“…Like these results, 88.7% of our intermediate risk patients were also free of disease at last evaluation. In the same way, in low or intermediate-risk patients a s-Tg may not be necessary when b-Tg defines the response as excellent 27 . Thus, these data together suggest that low or intermediate risk DTC patients with a pre-RAI Tg≤7.55 ng/ml may be initially evaluated only based on b-Tg together with neck US.…”

The effect of thyroid hormone withdrawal performed to evaluate the success of I-131 ablation on quality of life and psychological symptoms in female patients with low-risk differentiated thyroid cancer

“…We can only administer thyrotropin alfa to select patients with comorbidities who cannot tolerate hypothyroidism. It has already been reported that in patients with a lowintermediate risk of well-differentiated thyroid cancer, basal thyroglobulin has an important prognostic value in predicting treatment response and prognosis, stimulating thyroglobulin may not be needed due to its cost and side effects (29)(30)(31).…”