The combined evaluation of clinical and biochemical data in management of patients with differentiated thyroid cancer

Excerpt

Differentiated thyroid cancer (DTC) represents the most frequent endocrine neoplasm, accounting for 5% of thyroid nodules [1]. The standard treatment of patients with DTC consists of surgery followed by radioactive iodine (RAI) therapy [1]. Despite an excellent prognosis, with a 10-year overall survival rate near to 90%, a significant percentage of patients will show recurrence of disease during follow-up [2, 3]. The RAI therapy plays a substantial role in this context, and it can be administered in patients with known persistent disease, to reduce the tumor burden and improve prognosis. However, also in patients without evidence of disease after surgery, iodine-131 (¹³¹I) can be administered for remnant ablation, to ablate non-tumoral residual tissue and facilitate follow-up. In patients with suspected persistent disease after surgery, adjuvant RAI therapy can be performed in order to reduce the rate of recurrence [1, 3, 4]. Moreover, the post-therapy whole-body scan (WBS) acquired after ¹³¹I administration is able to detect the presence of disease improving initial staging in DTC patients [5‐7]. Actually, the indication for RAI administration is mainly based on the American Thyroid Association (ATA) guidelines; according to this initial risk stratification system, patients are classified as low, intermediate, or high risk of recurrence [1]. ATA stratification system has been validated in different cohorts of DTC patients [4, 8, 9]. It has been demonstrated that the persistence of structural disease is infrequent in low ATA–risk patients [4, 8]. Therefore, RAI administration is recommended in intermediate- and high-risk patients, and it can be avoided in low-risk subjects [10, 11]. It has been previously demonstrated that the ablation rate is higher in intermediate ATA–risk patients than in those classified as high ATA risk (71% vs. 52%) [4]. This evidence suggests that patients initially categorized as intermediate and high risk may have varied clinical outcomes, suggesting that further risk stratification markers are needed. Therefore, other clinical and biochemical data beyond traditional markers of disease are needed. Moreover, an accurate evaluation of disease status after surgical treatment may help in optimizing therapeutic protocols, respective to doses and treatment modalities. Thyroglobulin (Tg) is a specific marker of thyroid tissue that significantly decreases after surgery. However, the persistence of detectable Tg levels indicates the presence of residual viable thyroid cells that can be also related to primary tumor cells, nodal metastases not completely resected, or distant metastases [12‐14]. Therefore, Tg measurements may be used as additional markers to perform an accurate evaluation of disease status by hybrid positron emission tomography (PET) and computed tomography (CT) with 2-deoxy-2-[¹⁸F]-fluoro-D-glucose ([¹⁸F]-FDG PET/CT) [15‐17]. [¹⁸F]-FDG PET/CT has a high diagnostic accuracy in DTC patients with the absence of structural disease on conventional imaging and serum Tg level that progresses with time, in an absence of radioiodine uptake in DTC lesions and in metastatic disease [16‐20]. …