Endocrine Abstracts

Objectives: The clinical significance of antithyroglobulin antibody (TgAb) levels verified concomitantly with undetectable thyroglobulin (Tg) during the follow-up of patients with differentiated thyroid carcinoma remains under debate. The present study aimed to evaluate the presence and prognostic predictive value of TgAb during the follow-up of patients with differentiated thyroid carcinoma.

Methods: A retrospective cohort study was performed by reviewing the medical records of patients being followed up in a tertiary service, from 2000 to 2020. Measurement of Tg was performed by chemiluminescence (Cobas 601, Roche) and of TgAb by electrochemiluminescence (Liaison, Diasorin).

Results: Data from 868 patients diagnosed with papillary thyroid carcinoma were evaluated, including 62 patients (7.1%) who had detectable TgAb during follow-up, either preoperatively or postoperatively. Most are female (85%), white (81%), non-smokers (77%), mean age of 43.18 years, mean follow-up time of 94 months. There was no relationship between preoperative TgAb levels and worse prognostic characteristics at follow-up. A higher percentage of time with detectable TgAb after thyroidectomy was showed as a predictive factor to non-excellent response to therapy (P < 0.0001, OR 1.089; CL95% 1.045-1.135), and also, it was observed in carcinomas with angiolymphatic invasion (P = 0.002), extrathyroidal invasion (P = 0.015), lymph node metastases (P = 0.008) and distant metastases (P = 0.009), as well as in T3 and T4 tumors (P = 0.008). Patients with incomplete structural response had a higher percentage of time with detectable TgAb compared to patients with excellent response one year after thyroidectomy (P < 0.001) and current response (last assessment during follow-up) (P < 0.001). The majority of patients with detectable TgAb had antibody negative throughout the follow-up period (59%), 24.1% remained stable, 9.6% showed a tendency to decrease and 6.4% to increase, and in this last group, 100% of the patients presented incomplete structural response.

Conclusions: This study showed that preoperatively detected TgAb are not associate to a worse prognosis in patients with differentiated thyroid carcinoma. We found that not only the appearance or increase of TgAb, but also the presence of stable TgAb levels were indicative of disease persistence or recurrence. In contrast, significant decline in TgAb was associated with disease-free status. In conclusion, when TgAb was detected during follow-up, temporal evaluation was important for defining the trend of TgAb and the relation with the progression of the disease.