Positive Predictive Value of Serum Thyroglobulin Levels, Measured during the First Year of Follow-Up after Thyroid Hormone Withdrawal, in Thyroid Cancer Patients

Abstract

The follow-up of patients with papillary and follicular thyroid carcinoma after thyroidectomy and radioiodine ablation is mainly based on serum thyroglobulin (Tg) level deter-mination. The positive predictive value (PPV) of serum Tg level after thyroid hormone withdrawal, measured during the first 6-12 months of follow-up (initial off L-T(4) Tg), was studied in 256 consecutive differentiated thyroid cancer patients. All underwent a total thyroidectomy and 3.7 GBq (131)I ablation; 37 patients had an elevated initial off L-T(4) Tg level. This study focuses on these 37 patients, 9 of whom had a clinical recurrence. The present data confirm that in this selected cohort of patients, 74-185 MBq (131)I-total body scan (TBS) has no clinical interest in the initial work-up and during the subsequent follow-up because it was negative in all patients, except in one with recurrent disease. The PPV of initial serum off L-T(4) Tg level above 5 ng/ml and 10 ng/ml was 42% and 53%, respectively; this PPV was only 50% at the time of recurrence or subsequent control. This relatively low PPV is related to the low recurrence rate in this series of patients, despite a prolonged follow-up, and to the subsequent decrease of serum Tg level in 14 of 37 (38%) patients in the absence of any further treatment. In contrast, the PPV of the increasing slope of serum Tg levels obtained after thyroid hormone withdrawal (83%) was excellent. In conclusion, we confirm that (131)I-TBS has a limited interest for the follow-up of thyroid cancer patients. Follow-up should rely on serum Tg level and prognostic parameters; however, initial serum Tg may be produced by thyroid tissues of various significance, an increase at two consecutive determinations indicating disease progression and a decrease being related to late effects of therapy. The best PPV is brought by the slope of serum Tg levels.

Importance of Postoperative Stimulated Thyroglobulin Level at the Time of131I Ablation Therapy for Differentiated Thyroid Cancer

“…Also, Lee et al (2013) reported that, when high-dose 131 I remnant ablation is performed after total thyroidectomy, the stimulated Tg measurement and DxWBS that are usually performed 6-12 months after 131 I ablation therapy may be skipped in low-and intermediate-risk patients with postoperative stimulated Tg level of <2ng/ml and negative neck ultrasonography findings. Similarly, Baudin et al (2003) reported that, DxWBS with 131 I has a limited interest for the follow-up of thyroid cancer patients. Whereas, we demonstrated that, in 2 of 55 patients with low risk and Tg level of <2ng/mL DxWBS was scan(+) Tg(-) in our study.…”

Management Guidelines for Patients with Thyroid Nodules and Differentiated Thyroid Cancer: The American Thyroid Association Guidelines Taskforce

“…Serum thyroglobulin measurements are less sensitive in patients with small cervical lymph node metastases or less differentiated tumor (184,200). A rising unstimulated or stimulated serum thyroglobulin may indicate disease that is likely to become clinically apparent (201,202).…”

Carcinoma diferenciado de tireóide: avaliação inicial e acompanhamento

“…Este achado se deve ao fato de que o tratamento com iodo pode resultar em um lento processo de morte celular e atrofia do tecido residual, não representando, necessariamente, doença recorrente ou persistente, o que pode evitar tratamentos inapropriados com radioiodo (32). Por outro lado, o achado de níveis de Tg em elevação é preditor de doença, devendo ser tratado (39).…”

“…Em um estudo com 256 pacientes, realizado por Baudin e cols., a ultrassonografia cervical foi o método mais sensível para detecção de focos de neoplasia naqueles pacientes com Tg positiva (39). Para estes autores, a realização do RCT no final do primeiro ano não teve impacto diagnóstico.…”