Abstract
Serum thyroglobulin is used as part of the early postoperative assessment of differentiated thyroid cancer (DTC) since there is a clear relationship between an increased risk of recurrence and persistent disease after initial treatment and high postoperative stimulated thyroglobulin (ps-Tg) values. Thus, although ps-Tg above 10–30 ng/mL is considered an independent predictor of worse prognosis, the value that is associated with distant metastases is not defined. Thus, this was our objective. We selected 655 DTC patients from a nuclear medicine department database (Irmandade Santa Casa de Misericórdia de São Paulo, Brazil). All patients had received total thyroidectomy and radioactive iodine (RAI) therapy and had ps-Tg values higher than 10 ng/mL with negative anti-thyroglobulin antibodies. Then, we selected patients who presented post-therapy whole-body scan with pulmonary and/or bone uptake but with no mediastinum or cervical uptake. Patients with negative findings on functional imaging or any doubt on lung/bone uptake were submitted to additional exams to exclude another non-thyroid tumor. Of the 655 patients, 14.3% had pulmonary and 4.4% bone metastases. There was a significant difference in ps-Tg levels between patients with and without metastases (P<0.001). The cutoff value of ps-Tg was 117.5 ng/mL (sensitivity: 70.2%; specificity: 71.7%) for those with lung metastasis, and 150.5 ng/mL (sensitivity: 79.3%; specificity: 85%) for those with bone metastasis. The cutoff value for patients with eitherpulmonary or bone metastasis was 117.5 ng/mL (sensitivity: 70.2%; specificity: 83.7%). Our findings demonstrated that ps-Tg could predict distant metastasis in DTC patients. We identified a cutoff of 117.5 ng/mL with a high negative predictive value of 93.7%.
Highlights
Thyroid cancer is a rare neoplasia, accounting for about 1% of all cancers
As we were looking for high-risk patients with distant metastases, we initially selected just patients who had undergone total thyroidectomy and radioactive iodine (RAI) therapy and had postoperative stimulated thyroglobulin (ps-Tg) values higher than 10 ng/mL with negative antithyroglobulin antibodies
Postoperative serum thyroglobulin levels can be a predictor of persistent disease after surgery, according to the American Thyroid Association (ATA)’s guidelines, but the optimal cutoff value to guide decisions in terms of appropriate radioiodine dose has not yet been well established
Summary
Thyroid cancer is a rare neoplasia, accounting for about 1% of all cancers. It is the most common tumor among malignant endocrine neoplasms [1,2]. Statistical data show an increase in the incidence of thyroid cancer in recent decades [1,2]. Over the past 10 years, the incidence rate of thyroid cancer has increased by an average of 3.1% each year in the US [3]. The mortality rate is relatively stable [1,2,3,4], increasing, on average, only 0.7% per year between 2006 and 2015. The 5-year survival rate for thyroid cancer is 98.1% [3]. The overall response to treatment is frequently excellent, the rate of recurrent or persistent cases varies from 23 to 30% [5]
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