A cutoff thyroglobulin value suggestive of distant metastases in differentiated thyroid cancer patients

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%.

O ensaio de tiroglobulina com melhor sensibilidade funcional enquanto os pacientes tomam L-T4 substituirá a tiroglobulina estimulada pelo TSH no seguimento dos pacientes com câncer diferenciado da tiróide? / Will the thyroglobulin assay with lower functional sensitivity whilst the patients are on L-T4 treatment replace the TSH-stimulated thyroglobulin assay in the follow-up of patients with differentiated thyroid cancer?

O autor apresenta evidências recentes da literatura que mostram que ensaios de tiroglobulina sérica (sTg) com maior sensibilidade funcional apresentam a mesma qualidade que a obtenção da sTg estimulada por rhTSH ou hipotiroidismo, no seguimento de pacientes com câncer diferenciado de tiróide (CDT). Desta forma, propõe modificar a prática recomendada pelas diretrizes de sociedades internacionais para o seguimento desses pacientes (desenvolvidas enquanto os ensaios disponíveis apresentavam sensibilidade de 1 ng/mL), substituindo-se a obtenção da sTg estimulada por rhTSH ou hipotiroidismo pelo acompanhamento dos pacientes na vigência da terapia com L-T4 com a medida da sTg desde que se empreguem técnicas com sensibilidade funcional da ordem de 0,1-0,2 ng/mL.

The author reviews the literature on the new assays for serum thyroglobulin (sTg) presenting lower functional sensitivity and demonstrates that its use, whilst the patients are taking L-T4, presents better results than sTg following TSH stimulation in the follow-up of patients with differentiated thyroid carcinoma. Therefore, he suggests a revision on the guidelines for the follow-up of these patients (developed when the available assays present a sensitivity of 1 ng/mL), proposing the use of sTg assays with functional sensitivity of 0.1-0.2 ng/mL with the patients on L-T4 treatment instead of sTg stimulated by TSH.