The effect of preoperative thyroglobulin and antithyroglobulin levels on postoperative follow-up and prognosis in patients with differentiated thyroid carcinoma

Objective: Thyroid carcinomas are the most common endocrine malignancies in the world and the majority of these are differentiated thyroid cancers. Although the prognosis is generally good, recurrent disease may develop in years of follow-up and may have mortal consequences. Therefore, there is a need for careful long-term follow-up and the presence of parameters that can predict prognosis in the long term. In this context, although thyroglobulin and antithyroglobulin values are parameters used in disease follow-up, the value of preoperative values in predicting prognosis is still a virgin subject. In this study, we aimed to investigate the effect and significance of preoperative thyroglobulin (Tg) and antithyroglobulin (Anti-Tg) levels on prognosis in patients with differentiated thyroid carcinoma. Materials and Methods: We screened 2458 patients with differentiated thyroid carcinoma (DTC) diagnosed in our hospital between October 2017 and October 2023. Of these, those who underwent surgery and had Tg or Anti-Tg values measured in the preoperative period were identified. The risk classification specified in the 2015 updated guidelines of the American Thyroid Association (ATA) was used to determine the risk level of the patients in the follow-up and in this context, although Tg or Anti-Tg levels were measured in the preoperative period, 20 patients who did not have the necessary data for risk assessment in the pathology reports were excluded from the study and 179 patients with differentiated thyroid carcinoma (DTC) who met all criteria were included in the study. The preoperative Tg and anti-Tg levels of the patients were compared with the postoperative follow-up and it was investigated whether the high values in the preoperative period were associated with a prolongation in the fall time of the current levels in the postoperative period. Tg and Anti-Tg levels in the preoperative period were also evaluated in terms of the presence of metastatic disease, recurrence during follow-up or the presence of residual tissue. Postoperative ultrasonography US and scintigraphy results were used in the evaluation of recurrence and residual tissue. The preoperative Tg and anti-Tg levels of the patients were also investigated for correlation with the postoperative risk classification.The results of preoperative fine needle aspiration biopsy (FNAB) and postoperative pathology results were evaluated in terms of prediction of malignancy. Nodule characteristics determined by US in the preoperative period were compared with ATA risk assessment results in terms of their significance in reflecting malignancy and predicting prognosis. Demographic characteristics of the patients, presence of comorbid diseases that may affect mortality, serum TSH, free T3, free T4, Tg and Anti-Tg levels from preoperative period to 48th month postoperatively, biochemical parameters that may indicate additional comorbidities during and after the operation were also included in the study. The presence of recurrence or recidivism in the postoperative period, the number of months of recurrence and the treatment modalities (reoperation, RAI or TKI) were evaluated within the scope of the study. Results: Of the 179 DTK patients included in the study, 76.5 % were female and 23.5 % were male. The female to male ratio was approximately 3.2. The mean age of the patient population was 51.42 15.56 years. In our study, the time-dependent change in thyroglobulin averages of patients with and without recurrence from preoperative to 24th month was statistically significant (p<0.001). There was a significant difference in the change in thyroglobulin mean values of the patients in our study from the preoperative period to the postoperative 24th month in the groups with and without recurrence (p=0.002). In our study, the cut-off value for the discrimination of preoperative thyroglobulin value in case of recurrence was determined as 100.10 ng/ mL. This value was considered statistically borderline significant (p=0.063). In our study, the time-dependent change in antithyroglobulin averages from preoperative to 24th month was not statistically significant in the recurrence and non-recurrence groups (p=0.587). The change in the mean antithyroglobulin levels from the preoperative period to the 24th month postoperatively was similar in the recurrence and non-recurrence groups (p=0.341). Conclusion: Preoperative thyroglobulin levels are a significant parameter in predicting prognosis and determining the risk of recurrent disease. Although antithyroglobulin alone does not have sufficient prognostic significance to indicate the presence of recurrent disease, it is a parameter that should be evaluated together with thyroglobulin in the follow-up of DTK due to its interference with thyroglobulin. The presence of recurrence was associated with the adequacy of the operation rather than preoperative tumor behavior characteristics. Keywords: Thyroglobulin, Antithyroglobulin, Differentiated Thyroid Carcinoma, Recurrence, Residual Tissue