Clinical Utility of 18F-FDG PET/CT Concurrent with 131I Therapy in Intermediate–to–High-Risk Patients with Differentiated Thyroid Cancer: Dual-Center Experience with 286 Patients

The impact of qualitative [18F]FDG PET/CT in predicting clinical outcomes of post-surgical differentiated thyroid cancer patients with elevated thyroglobulin and negative radioiodine whole-body scan

BACKGROUND

[18F]FDG PET/CT has been widely used as a diagnostic tool in detection and localization of recurrent non-avid radioiodine lesions in post-operative differentiated thyroid cancer (DTC) patients with elevated serum thyroglobulin but negative radioiodine whole-body scan (TENIS) syndrome. The aim of our study was to evaluate the role of [18F]FDG PET/CT in prediction on outcomes of these DTC patients.

METHODS

Post-operative DTC patients with TENIS syndrome were collected in the department of nuclear medicine, Hospital 108 from 2019 to 2023. Patients underwent [18F]FDG PET/CT with standard protocol following EANM guideline for tumor imaging version 2.0. The qualitative [18F]FDG PET/CT imaging characteristics were classified into three categories: (i) negative [18F]FDG PET/CT, (ii) minimal [18F]FDG PET/CT volume of lesions, (iii) extensive [18F]FDG PET/CT volume of lesions. Progression-free survival (PFS) and overall survival (OS) were the end point of the study. The prognosis of qualitative [18F]FDG PET/CT in predicting PFS and OS was illustrated by Kaplan-Meier survival analysis. The independent factors predicting PFS and OS were determined by univariate and multivariate analysis using logistic regression.

RESULTS

There were 164 consecutive patients, 51.2% female and 48.8% female. The most common histopathological type was papillary accounting for 91.5%. The median time of follow-up was 33.3 months, (range 6.57 - 82.5). There was 70 (36.6%) progressions and 12 (7.35%) deaths. Negative [18F]FDG PET/CT uptake patients had median PFS with median 57.1 months which was higher than that of minimal category (46.2 months), and extensive category (37.6 months) (p < 0,001). 1-year OS and 5-year OS in extensive PET/CT category was 97.8% and 86.2% respectively which were significantly lower than that of negative and minimal categories (p = 0.053). In multivariate analysis, age at the time of diagnosis, pulmonary, bone metastases and extensive [18F]FDG PET/CT volume of lesions were the independent factor predicting PFS. Bone metastasis was only the factor could predict OS in multivariate analysis.

CONCLUSIONS

The minimal and negative [18F]FDG PET/CT categories had better prognosis than extensive category in PFS and OS. Extensive [18F]FDG PET/CT category was an independent factor for predicting PFS. Bone metastasis was only the independent factor that could predict both PFS and OS.

Role of [18F]FDG PET/CT in the management of follicular cell-derived thyroid carcinoma

Follicular cell-derived thyroid carcinomas constitute the majority of thyroid malignancies. This heterogeneous group of tumours includes well differentiated, poorly differentiated, and undifferentiated forms, which have distinct pathological features, clinical behaviour, and prognosis. Positron emission tomography with 2-[18F]fluoro-2-deoxy-D-glucose combined with computed tomography ([18F]FDG PET/CT) is an imaging modality used in routine clinical practice for oncological patients. [18F]FDG PET/CT has emerged as a valuable tool for identifying patients at high risk of poor clinical outcomes and for facilitating individualized clinical decision-making. The aim of this comprehensive review is to summarize current knowledge regarding the role of [18F]FDG PET/CT in primary diagnosis, treatment, and follow-up of follicular cell-derived thyroid carcinomas considering the degree of differentiation. Controversial issues, including significance of accidentally detected [18F]FDG uptake in the thyroid, the role of [18F]FDG PET/CT in the early assessment of response to molecular targeted therapies, and its prognostic value are discussed in detail.

Positron Emission Tomography/Computed Tomography in Thyroid Cancer: An Updated Review

PET/computed tomography (CT) is a valuable hybrid imaging modality for the evaluation of thyroid cancer, potentially impacting management decisions. 18F-fluorodeoxyglucose (FDG) PET/CT has proven utility for recurrence evaluation in differentiated thyroid cancer (DTC) patients having thyroglobulin elevation with negative iodine scintigraphy. Aggressive histologic subtypes such as anaplastic thyroid cancer shower higher FDG uptake. 18F-FDOPA is the preferred PET tracer for medullary thyroid cancer. Fibroblast activation protein inhibitor and arginylglycylaspartic acid -based radiotracers have emerged as promising PET agents for radioiodine refractory DTC patients with the potential for theranostic application.

Current practice in intermediate risk differentiated thyroid cancer - a review

Although the overall prognosis for differentiated thyroid cancer (DTC) is excellent, a subset of patients will experience disease recurrence or may not respond to standard treatments. In recent years, DTC management has become more personalized in order to enhance treatment efficacy and avoid unnecessary interventions.In this context, major guidelines recommend post-surgery staging to assess the risk of disease persistence, recurrence, and mortality. Consequently, risk stratification becomes pivotal in determining the necessity of postoperative adjuvant therapy, which may include radioiodine therapy (RIT), the degree of TSH suppression, additional imaging studies, and the frequency of follow-up.However, the intermediate risk of recurrence is a highly heterogeneous category that encompasses various risk criteria, often combined, resulting in varying degrees of aggressiveness and a recurrence risk ranging from 5 to 20%. Furthermore, there is not enough long-term prognosis data for these patients. Unlike low- and high-risk DTC, the available literature is contradictory, and there is no consensus regarding adjuvant therapy.We aim to provide an overview of intermediate-risk differentiated thyroid cancer, focusing on criteria to consider when deciding on adjuvant therapy in the current context of personalized approach, including molecular analysis to enhance the accuracy of patient management.

How [18F]FDG-PET/CT Affects the Management of Patients with Differentiated Thyroid Carcinoma in Clinical Routines

PURPOSE

To investigate the impact of [18F]FDG-PET/CT on the management of differentiated thyroid carcinoma (DTC) in routine clinical settings.

MATERIAL AND METHODS

In total, 98 patients (55 females, age 56 ± 18 years) with histologically confirmed thyroid cancer, including all types of DTC and poorly differentiated thyroid cancer (PDTC, n = 7), underwent [18F]FDG-PET/CT for staging or recurrence diagnostics performed using a state-of-the art clinical scanner (Biograph mCT, Siemens Healthineers) with a standardized examination protocol. The impact of PET/CT on clinical decision making was prospectively evaluated using standardized questionnaires completed by the referring physicians before and after PET/CT. Patient outcome was analyzed for OS drawn from patient records.

RESULTS

Referring physicians were unable to establish a treatment plan for 81% of patients with thyroid cancer in the absence of PET/CT. The use of PET/CT had a notable influence on patient management, leading to the development of a well-defined treatment plan for 92% of patients. Moreover, after PET/CT a change in pre-PET/CT-intended treatments occurred in 32% of cases, and further invasive diagnostic could be waived in 7% of cases. [18F]FDG-PET/CT revealed a tumor detection rate of 68% (local tumor: 19%, lymph node metastases: 40%, distant metastases: 42%). HTg levels, when stimulated via TSH, were considerably higher in patients with metastases detected on PET/CT, compared to those without metastatic findings (p = 0.02). OS was significantly worse in patients with PDTC (p = 0.002) compared to follicular thyroid cancer (FTC) and PTC or even in patients with distant metastases at first diagnosis (p = 0.03).

CONCLUSIONS

This prospective registry study confirms that [18F]FDG-PET/CT used in a routine clinical setting has a very important impact on the management of patients with thyroid cancer by initiating treatments and reducing the uses of additional imaging and invasive tests.

Tumor Microenvironment Features as Predictive Biomarkers in Metastatic Differentiated Thyroid Cancer and Their Relationship With 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (18F-FDG PET/CT) Metabolic Parameters

OBJECTIVE

The role of the tumor microenvironment in tumor progression and treatment response is being investigated for different types of cancer. This study aimed to determine the relationships between tumor microenvironment, histopathology, 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT)-based metabolic parameters, treatment response, and overall survival (OS) in metastatic differentiated thyroid cancer (DTC).  Methods: Metastatic DTC patients who underwent 18F-FDG PET/CT between 2015-2019 were evaluated. Clinicopathological, histopathological features and PET/CT parameters of patients were recorded. Microenvironmental characteristics of the primary tumor, such as mitosis, intratumoral and peritumoral lymphocytosis, intratumoral and peritumoral fibrosis, were evaluated from the tissue samples. The relationships between these factors were statistically analyzed.

RESULTS

 Sixty-five patients (38 females, 27 males, age: 49±15 years) were included. Mitosis, intra/peritumoral lymphocytosis, and intra/peritumoral fibrosis were frequent; however, none of them had a statistically significant association with PET-positive metastases, treatment response, or OS. Univariate analysis showed that gender, size, thyroglobulin values, residual thyroid tissue, PET-positive metastases, and maximum standardized uptake value (SUVmax) were significant predictors of OS. At multivariate analysis, PET-positive metastases (HR=-2.65, 95%CI 0.007-0.707, p=0.024) and SUVmax (HR=-2.74, 95%CI 0.006-0.687, p=0.023) were the only independent predictors for OS.  Conclusion: Our study revealed that microenvironmental characteristics of the primary tumor did not show prognostic significance in metastatic DTC. PET-positive metastases and SUVmax levels were the only significant factors that predicted overall survival in DTC. Supporting the results of our study with further studies with a larger sample size may be necessary to determine the relationship between the tumor microenvironment and prognosis in DTC.

Diagnostic significance of MRI versus CT using identical PET data in patients with recurrent differentiated thyroid cancer: A PET/MRI study

In this retrospective study we compared magnet resonance imaging (MRI) and computed tomography (CT) each combined with identical 2-deoxy-2-[18F] fluoro-D-glucose or 2-[18F] F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) data in patients with recurrent differentiated thyroid cancer (DTC). In total 42 patients with DTC were examined. All patients underwent FDG PET/MRI and CT, the latter originating from one of the following examinations: I-131 single photon emission computed tomography/CT (32/42), low dose FDG PET/CT (5/42) or diagnostic FDG PET/CT (5/42). Two readers assessed FDG PET/MRI as well as FDG PET/CT, with the latter CT coming from one of the above examinations performed at a maximum temporal interval of 5 days from PET/MRI. Local recurrence, cervical lymph node - and pulmonary metastases were assessed in a consensus read. Lesions rated with a high malignancy score (score 4 or 5) were further analyzed. Every malignant lesion was verified if it was identified by one of both or by both modalities. In 20 of 42 patients altogether 100 malignant lesions were present. In 11/20 patients in total 15 local recurrences (15 in MRI/ 9 in CT: 9 CT/MRI, 6 MRI only, 0 CT only; P = .04) were found with a statistically significant better performance of MRI. Regarding lymph node metastases, in total 13 lesions (12 in MRI/ 8 in CT: 7 CT/MRI, 5 MRI only, 1 CT only; P = .22) in 8/20 patients were found with no significant difference between both modalities. Furthermore, in 9/20 patients in total 72 lung lesions (40 in MRI/ 63 in CT: 31 CT/MRI, 9 MRI only, 32 CT only; P = .001) were found with a statistically significant better performance of CT. In 33/42 patients follow up was available and supported the observations. In patients with recurrent DTC, PET/MRI showed superiority compared to PET/CT in evaluation of the neck region. PET/MRI was inferior to PET/CT in evaluation of the lung. PET/MRI in combination with a low dose CT of the lung may thus represent the ideal staging tool in patients with recurrent DTC.

Role of PET/Computed Tomography in Elderly Thyroid Cancer: Tumor Biology and Clinical Management

PET/computed tomography (CT) studies can be potentially useful in elderly thyroid carcinoma patients for exploring the disease biology, especially in metastatic setting and thereby directing appropriate therapeutic management on case-to-case basis, adopting nuclear theranostics, and disease prognostication. With the availability of multiple PET radiopharmaceuticals, it would be worthwhile to evolve and optimally use FDG and the other non-fluorodeoxyglucose and investigational PET/CT tracers as per the clinical situation and need and thereby define their utilities in a given case scenario. In this regard, (I) differentiated thyroid carcinoma (DTC) including radioiodine refractory disease, poorly differentiated thyroid cancer (PDTC) and TENIS, (II) medullary thyroid carcinoma (MTC), (III) anaplastic carcinoma and (IV) Primary thyroid lymphoma (PTL) should be viewed and dealt separately.

Towards an era of precise diagnosis and treatment: Role of novel molecular modification-based imaging and therapy for dedifferentiated thyroid cancer

Dedifferentiated thyroid cancer is the major cause of mortality in thyroid cancer and is difficult to treat. Hence, the essential molecular mechanisms involved in dedifferentiation should be thoroughly investigated. Several studies have explored the biomolecular modifications of dedifferentiated thyroid cancer such as DNA methylation, protein phosphorylation, acetylation, ubiquitination, and glycosylation and the new targets for radiological imaging and therapy in recent years. Novel radionuclide tracers and drugs have shown attractive potential in the early diagnosis and treatment of dedifferentiated thyroid cancer. We summarized the updated molecular mechanisms of dedifferentiation combined with early detection by molecular modification-based imaging to provide more accurate diagnosis and novel therapeutics in the management of dedifferentiated thyroid cancer.

Follicular thyroid carcinoma metastasizing to rare sites and exhibiting variable inter-lesional heterogeneity on 18F-fluorodeoxyglucose positron emission tomography/computed tomography and 131I

A patient of differentiated follicular thyroid carcinoma with unusual sites of metastases is illustrated with ¹³¹I and ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) imaging findings. The described case harbored extremely rare metastasis to the urinary bladder with multi-organ metastatic disease (including unusual sites of right bronchus and hepatic metastases). There was inter-lesional heterogeneity among the metastatic lesions with regard to the ¹³¹I and FDG uptake in the aforementioned lesions. The detection of such heterogeneity has important implications for patient management in metastatic differentiated thyroid carcinoma.

Investigating 18F-FDG PET/CT Parameters as Prognostic Markers for Differentiated Thyroid Cancer: A Systematic Review

Aims: The aim of this study was to determine whether ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) parameters might be prognostic markers for patients with differentiated thyroid carcinoma (DTC).

Methods: We searched for eligible articles in PubMed, EMBASE (Ovid), Cochrane Library, and ClinicalTrials.gov from inception to February 2021. We included studies addressing the association between ¹⁸F-FDG PET/CT parameters and clinical outcomes among patients with DTC. Quality assessment was performed using the Quality in Prognosis Studies (QUIPS) tool.

Results: A total of 25 studies including 2,954 patients (1,994 females, 67.5%) were included; 2,416 patients (81.8%) had papillary thyroid carcinoma (PTC), and the mean or median follow-up time ranged from 19.1 months to 17.1 years. Thirteen (52.0%) studies were assessed as “unclear” for the domain of study participation. The most common timing of PET/CT scans was after thyroidectomy (in 20 of 25 studies, 80%), especially in patients with an elevated thyroglobulin (Tg) and a negative radioiodine whole-body scan (WBS). The most common PET parameter was FDG uptake. Twelve of 17 (70.6%) and 12 of 12 (100%) studies showed an association between PET/CT parameters and disease progression and survival in patients with DTC, respectively.

Conclusion:¹⁸F-FDG PET/CT parameters alone or combined with other variables can serve as prognostic markers to identify DTC patients with poor outcomes, especially in the setting of an elevated Tg and a negative WBS. Future research is needed to confirm these findings and to examine the prognostic value of PET/CT parameters for DTC patients, considering the heterogeneity in PET/CT parameters, unclear information of patients, and PET/CT-adapted treatment modifications.

PET/CT in the management of differentiated thyroid cancer

The standard treatment of differentiated thyroid cancer (DTC) consists of surgery followed by iodine-131 (¹³¹I) administration. Although the majority of DTC has a very good prognosis, more aggressive histologic subtypes convey a worse prognosis. Follow-up consists of periodically measurements of serum thyroglobulin, thyroglobulin antibodies and neck ultrasound and ¹²³I/¹³¹I whole-body scan. However, undifferentiated thyroid tumors have a lower avidity for radioiodine and the ability of DTC to concentrate ¹³¹I may be lost in metastatic disease. Positron emission tomography (PET)/computed tomography (CT) has been introduced in the evaluation of patients with thyroid tumors and the 2-[18F]-fluoro-2-deoxyd-glucose (¹⁸F-FDG) has been largely validated as marker of cell's metabolism. According to the 2015 American Thyroid Association guidelines, ¹⁸F-FDG PET/CT is recommended in the follow-up of high-risk patients with elevated serum thyroglobulin and negative ¹³¹I imaging, in the assessment of metastatic patients, for lesion detection and risk stratification and in predicting the response to therapy. It should be considered that well-differentiated iodine avid lesions could not concentrate ¹⁸F-FDG, and a reciprocal pattern of iodine and ¹⁸F-FDG uptake has been observed. Beyond ¹⁸F-FDG, other tracers are available for PET imaging of thyroid tumors, such as Iodine-124 (¹²⁴I), ¹⁸F-tetrafluoroborate and Gallium-68 prostate-specific membrane antigen. Moreover, the recent introduction of PET/MRI, offers now several opportunities in the field of patients with DTC. This review summarizes the evidences on the role of PET/CT in management of patients with DTC, focusing on potential applications and on elucidating some still debating points.

Impact of FDG-PET on therapy management and outcome of differentiated thyroid carcinoma patients with elevated thyroglobulin despite negative iodine scintigraphy

AIM

 The objective of this study was to assess the impact of implementing FDG-PET imaging in treatment algorithms for differentiated thyroid cancer with suspected recurrence. Primary end points were overall, event-free and disease-specific survival. Secondary end points were therapies, disease control and the sensitivity and specificity of PET imaging.

METHODS

 194 patients with DTC treated at our center from 1996 to 2014 following thyroidectomy and routine 131I ablation with no remaining 131I uptake in whole-body scans but persisting or rising thyroglobulin values were enrolled in this retrospective analysis. Of these, 149 (76.8 %) received an 18F-FDG scan (PET group) whereas the remaining 45 patients (23.2 %) did not (non-PET group). Survival, disease-specific characteristics at inclusion, disease control and therapies were compared.

RESULTS

 Patients of the PET group generally showed characteristics associated with higher disease activity from inclusion onwards. This did not translate to statistically significant differences in survival. If PET imaging was performed following inclusion, patients received significantly less radioiodine treatments during the first nine months after inclusion (63.1 % of the PET-group vs 82.2 % of the non-PET group). Simultaneously, patients tended to receive more surgeries following PET imaging (27.5 % PET-group vs 13.3 % non-PET group). No significant differences regarding disease control were observed.

CONCLUSION

 The early use of FDG-PET imaging in cases of suspected recurrence or existence of dedifferentiated DTC can lead to changes in therapy management, specifically identifying patients unlikely to benefit from additional radioiodine therapy who would instead qualify for surgical therapy methods.

The substance P and neurokinin-1 receptor system in human thyroid cancer: an immunohistochemical study

To develop a new therapeutic strategy against thyroid cancer (TC), the expression of both substance P (SP) and neurokinin-1 receptor (NK-1R) must be demonstrated in TC cells. This study aims to examine by immunohistochemistry, the localization of SP and the NK-1R in human TC samples (papillary, follicular, medullary, anaplastic), in metastasis and in healthy thyroid samples. SP and the NK-1R were expressed in all normal and TC samples. In healthy glands, SP was located in follicular cells (nucleus) and colloid and NK-1R in follicular cells (cytoplasm) and stroma. In TC samples, SP was visualized in follicular cells (nucleus and cytoplasm), stroma and colloid and NK-1R in follicular cells (cytoplasm), stroma and colloid. A semiquantitative scoring system (Allred Unit Scoring System) was applied. The expression (Allred total score) of SP and NK-1R was weaker in normal thyroid glands than in TC. In comparison with TC samples, a lower intensity/proportion of SP (nucleus and cytoplasm of follicular cells; stroma) was observed in normal samples. By contrast, in the colloid of TC samples the presence of SP was lower than in normal samples. In comparison with TC samples, the presence of the NK-1R in the cytoplasm of follicular cells and colloid was lower in normal thyroid samples, whereas the expression of this receptor in the stroma was higher. The results reported in this study suggest that the NK-1R could be a new target for the treatment of TC and use of the NK-1R antagonists could serve as a new anti-TC therapeutic strategy.

PROGNOSTIC VALUE OF LYMPH NODE UPTAKE ON PRETREATMENT F-18 FDG PET/CT IN PATIENTS WITH N1B PAPILLARY THYROID CARCINOMA

Objective: The aim of this study was to investigate the prognostic value of metabolic characteristics of metastatic lymph node (LN) using pretreatment F-18 fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) for patients with papillary thyroid carcinoma (PTC) and metastatic lateral LN (N1b). Methods: Ninety-six PTC patients (female:male = 72:24; median age, 44.5 years) with pathologic N1b who underwent pretreatment FDG PET/CT, total thyroidectomy, and radioactive iodine ablation were retrospectively reviewed. To predict responses to initial therapy and recurrence, clinicopathologic factors and metabolic parameters were reviewed, such as sex, age, tumor size, extranodal extension, number and ratio of metastatic LNs, serum thyroglobulin, and maximum standardized uptake value (SUVmax). Results: Among the 96 PTC patients, 81 (84.4%) were classified into the acceptable response (58 excellent; 23 indeterminate) and 15 (15.6%) into the incomplete response (8 biochemical incomplete; 7 structural incomplete) by the 2015 American Thyroid Association management guideline for differentiated thyroid carcinoma. The multivariate analysis showed that SUVmax of N1b (P = .018), pre-ablation stimulated thyroglobulin level (P = .006), and the ratio of metastatic LNs (P = .018) were related to incomplete response. The cutoff value of each variable was determined by receiver operating characteristic analysis. Nine (9.4%) patients experienced recurrences (median follow-up: 50 months). The Kaplan-Meier analysis revealed that SUVmax of N1b (cutoff value: 2.3; P = .025) and ratio of metastatic LNs (cutoff value: 0.218; P = .037) were significant prognostic factors for recurrence. Conclusion: High SUVmax of N1b cervical LN on pretreatment FDG PET/CT could predict incomplete responses to initial therapy and recurrence in patients with N1b PTC. Abbreviations: ATA = American Thyroid Association; DTC = well-differentiated thyroid carcinoma; FDG = F-18 fluorodeoxyglucose; IQR = interquartile range; LN = lymph node; N1b = metastatic lateral cervical lymph node; PET/CT = positron emission tomography/computed tomography; PTC = papillary thyroid carcinoma; RAI = radioactive iodine; ROC = receiver operating characteristic; SUVmax = maximum standardized uptake value; Tg = thyroglobulin; USG = ultrasonography.

Risk factors of malignant fluorodeoxyglucose-avid lymph node on preablation positron emission tomography in patients with papillary thyroid cancer undergoing radioiodine ablation therapy

F-18 fluorodeoxyglucose (FDG)-avid metastatic lesions are associated with a poor response to radioiodine ablation therapy (RIT) in papillary thyroid cancer (PTC). This study evaluated the significance of preablative FDG positron emission tomography (PET) for the assessment of risk factors and frequency of malignant FDG-avid lymph nodes in patients with PTC undergoing RIT.The study included 339 consecutive patients (mean age 46.3 ± 12.5 y; 260 females) with PTC referred for the first RIT and who underwent routine preablative FDG PET between April 2011 and February 2013. FDG-avid lymph nodes (FALNs) were identified using retrospective image reviews. The frequency of malignant FALN (mFALN), its contribution to persistent or recurrent PTC, and its risk factors were analyzed.Among the patients, 112 had FALNs (33.0%): 11 mFALNs (3.2%) and 101 benign FALNs (bFALNs, 29.8%). mFALN contributed to 55% of persistent or recurrent PTC after RIT, which was observed in 20 of 339 patients (5.9%) during the post-RIT follow-up. Among preoperative risk factors, suspicious extrathyroidal extension and lateral neck lymph node metastasis on imaging studies were associated with mFALN. Among postoperative risk factors, T3/T4 and N1b stages, higher stimulated thyroglobulin, and higher numbers of metastatic lymph nodes and dissected lymph nodes, were associated with mFALN.mFALNs were observed in a small number of patients with PTC undergoing RIT, but it contributed 55% of total recurrent or persistent disease. Increased frequency of mFALNs is associated with more advanced PTC. Preablative FDG PET has value in evaluation of patients with RIT-resistant lesions and may help determine further treatment strategies.

Surveillance for Differentiated Thyroid Cancer Recurrence

Serum thyroglobulin monitoring along with anatomic and functional imaging play key roles in the surveillance of patients with differentiated thyroid cancer after initial treatment. Among patients with a disease stage justifying thyroid remnant ablation or with suspected metastatic disease, radioiodine whole-body scans are essential in the months after surgery. For patients with low to moderate-risk cancers, ultrasonography of the neck (with measurement of serum thyroglobulin on thyroid hormone replacement) are the best initial diagnostic modalities, and are often the only tests required. In individuals suspected of having distant metastases, CT, MRI, and 18F-FDG PET can make important contributions in localizing residual disease and monitoring its progression and responses to therapy, provided they are used in the appropriate setting.

Relationship Between 18F-fluorodeoxyglucose Accumulation and the BRAF V600E Mutation in Papillary Thyroid Cancer

BACKGROUND

To determine whether ¹⁸F-fluoro-2-deoxyglucose (¹⁸F-FDG)-PET/CT is useful for predicting the BRAF ^V600E mutation status of a primary papillary thyroid carcinoma (PTC).

METHODS

A retrospective analysis was performed in 108 patients who underwent ¹⁸F-FDG positron emission tomography-computed tomography (PET/CT) for staging before thyroidectomy and BRAF analysis in biopsy-confirmed PTC. The maximum standardized uptake value (SUV_max) of the primary tumor was calculated according to FDG accumulation. Univariate and multivariate analyses were performed to assess the association between the SUV_max and clinicopathological variables.

RESULTS

The BRAF ^V600E mutation was detected in 71 of 108 (65.7%) patients. In all subjects, the tumor size and BRAF ^V600E mutation were independently related to the SUV_max according to multivariate analyses (P = 0.002 and 0.007, respectively). The SUV_max was significantly higher in tumors with the BRAF ^V600E mutation than in tumors with wild-type BRAF (10.24 ± 11.89 versus 4.02 ± 3.86; P = 0.007). In the tumor size >1 cm subgroup, the BRAF ^V600E mutation was the only factor significantly associated with the SUV_max (P = 0.016). A SUV_max cutoff level of 4.9 was determined to be significant for predicting the BRAF ^V600E mutation status (sensitivity 77.4%, specificity 100.0%, area under the curve 0.929; P < 0.0001) according to ROC curve analysis.

CONCLUSIONS

The BRAF ^V600E mutation is independently associated with high ¹⁸F-FDG uptake in PTC, especially in those with a tumor size >1 cm.

Predicting 131I-avidity of metastases from differentiated thyroid cancer using 18F-FDG PET/CT in postoperative patients with elevated thyroglobulin

The quantitative relationship between iodine and glucose metabolism in metastases from differentiated thyroid cancer (DTC) remains unknown. Aim of the prospective study was to establish the value of ¹⁸F-FDG PET/CT in predicting ¹³¹I-avidity of metastases from DTC before the first radioiodine therapy. A total of 121 postoperative DTC patients with elevated stimulated serum thyroglobulin (ssTg) who underwent ¹³¹I adjuvant therapy or therapy after ¹⁸F-FDG PET/CT scan were enrolled. The Receiver operating characteristic curve was established to create an optimal cut-off point and evaluate the value of SUVmax for predicting ¹³¹I-avidity. In our study, the median SUVmax in ¹³¹I-nonavid metastatic target lesions was also significantly higher than that in ¹³¹I-avid metastatic target lesions (5.37 vs. 3.30; P = 0.000). At a cut-off value of 4.0 in SUVmax, the area under curve was 0.62 with the sensitivity, specificity, positive predictive value and negative predictive value of 75.3%, 56.7%, 76.1%, and 54.8%, respectively. These results suggest that ¹⁸F-FDG PET/CT may be of great value in identifying metastases in postoperative DTC patients with elevated ssTg before ¹³¹I administration, leading to an improved management of disease. ¹⁸F-FDG positive metastatic DTC with SUVmax of greater than 4.0 possesses higher probability of non-avidity to radioiodine.

Initial [18F]FDG PET/CT in high-risk DTC patients

In a previous paper, we published the impact of initial [18F]FDG PET/CT (FDG-PET/CT) in high-risk patients with differentiated thyroid cancer (DTC) and described the changes in therapy management. The aim of the present study was to evaluate the prognostic impact of the initial FDG-PET/CT on a patient’s follow-up over three years and the rate of complete remission. Patients, methods: This study included 109 DTC patients who underwent radioiodine treatment (RIT), including posttherapeutic whole-body scintigraphy with FDG-PET/CT and a follow-up over three years. The follow-up included high-resolution sonography of the neck and determination of serum Tg as well as Tg antibodies every six months. The results of initial FDG-PET/CT and whole-body scintigraphy were compared with the status after three years of follow-up. Results: 24/109 patients (22%) presented FDG-positive lesions, 22/109 patients (20%) only iodine-positive lesions, and 63/109 patients (58%) neither FDG-positive nor iodine-positive lesions. After three years, 83/109 patients (76%) revealed full remission, 15/109 patients (14%) tumour persistence and 11/109 patients (10%) a progressive disease. The negative predictive value (NPV) was calculated for patients without FDG-positive lesions (NPV 85%) and patients without any lesions (NPV 91%) regarding full remission in the follow-up. Conclusion: FDG-PET/CT has a high NPV (85% to 91%) in DTC patients regarding recurrence-free follow-up after three years. The change in patient management in patients with iodine-negative lesions can lead to a higher rate of full remissions in the follow-up after additional surgery. Therefore, FDG-PET/ CT should be performed in all high-risk DTC patients in the context of the first RIT to improve patient management and risk stratification.

Clinical utility of 18F-FDG PET/CT in the follow-up of a large cohort of patients with high-risk differentiated thyroid carcinoma

OBJECTIVE

To evaluate the clinical utility of 18F-FDG PET/CT in patients with high-risk DTC.

SUBJECTS AND METHODS

Single-center retrospective study with 74 patients with high-risk differentiated thyroid cancer (DTC), classified in 4 groups. Group 1: patients with positive sTg or TgAb, subdivided in Group 1A: negative RxWBS and no foci of metastases identified at conventional image (n = 9); Group 1B: RxWBS not compatible with suspicious foci at conventional image or not proportional to sTg level (n = 13); Group 2: patients with histological findings of aggressive DTC variants (n = 21) and Group 3: patients with positive RxWBS (n = 31).

RESULTS

18F-FDG PET/CT identified undifferentiated lesions and helped restage the disease in groups 1B and 2. The scan helped guide clinical judgment in 9/13 (69%) patients of group 1B, 10/21 (48%) patients of group 2 and 2/31 (6%) patients of group 3. There was no clinical benefit associated with group 1A. 18F-FDG PET/CT was associated with progressive disease.

CONCLUSION

18F-FDG PET/CT is a useful tool in the follow-up of patients with high-risk DTC, mainly in the group of RxWBS not compatible with suspicious foci at conventional image or not proportional to sTg level and in those with aggressive DTC variants. Additionally, this study showed that 18F-FDG PET/CT was associated with progression and helped display undifferentiated lesions guiding clinical assessments regarding surgeries or expectant treatments.

ENDOCRINE TUMOURS: Imaging in the follow-up of differentiated thyroid cancer: current evidence and future perspectives for a risk-adapted approach

The clinical and epidemiological profiles of differentiated thyroid cancers (DTCs) have changed in the last three decades. Today's DTCs are more likely to be small, localized, asymptomatic papillary forms. Current practice is, though, moving toward more conservative approaches (e.g. lobectomy instead of total thyroidectomy, selective use of radioiodine). This evolution has been paralleled and partly driven by rapid technological advances in the field of diagnostic imaging. The challenge of contemporary DTCs follow-up is to tailor a risk-of-recurrence-based management, taking into account the dynamic nature of these risks, which evolve over time, spontaneously and in response to treatments. This review provides a closer look at the evolving evidence-based views on the use and utility of imaging technology in the post-treatment staging and the short- and long-term surveillance of patients with DTCs. The studies considered range from cervical US with Doppler flow analysis to an expanding palette of increasingly sophisticated second-line studies (cross-sectional, functional, combined-modality approaches), which can be used to detect disease that has spread beyond the neck and, in some cases, shed light on its probable outcome.

Analysis of predictability of F-18 fluorodeoxyglucose-PET/CT in the recurrence of papillary thyroid carcinoma

Whether preoperative F-18 fluorodeoxyglucose (FDG)-positron emission tomography/computed tomography (PET/CT) can predict recurrence of papillary thyroid carcinoma (PTC) remains unclear. Herein, we evaluated the potential of primary tumor FDG avidity for the prediction of tumor recurrence in PTC patients. A total of 412 PTC patients (72 males, 340 females; age: 47.2 ± 12.2 years; range: 17-84 years) who underwent FDG-PET/CT prior to total thyroidectomy (n = 350), subtotal thyroidectomy (n = 2), or lobectomy (n = 60) from 2007 to 2011 were analyzed. The predictive ability for recurrence was investigated among various clinicopathological factors, BRAFV600E mutation, and preoperative FDG avidity of the primary tumor using Kaplan-Meier (univariate) and Cox proportional hazards regression (multivariate) analyses. Of the 412 patients, 19 (4.6%) experienced recurrence, which was confirmed either by pathology (n = 17) or high serum thyroglobulin level (n = 2), during a mean follow-up period of 43.9 ± 16.6 months. Of the 412 patients, 237 (57.5%) had FDG-avid tumors (maximum standardized uptake value, 7.1 ± 7.0; range: 1.6-50.5). Kaplan-Meier analysis revealed that tumor size (P = 0.0054), FDG avidity of the tumor (P = 0.0049), extrathyroidal extension (P = 0.0212), and lymph node (LN) stage (P < 0.0001) were significant predictors for recurrence. However, only LN stage remained a significant predictor in the multivariate analysis (P < 0.0001). Patients with FDG-avid tumors had higher LN stage (P < 0.0001), larger tumor size (P < 0.0001), and more frequent extrathyroidal extension (P < 0.0001). In conclusion, FDG avidity of the primary tumor in preoperative FDG-PET/CT could not predict the recurrence of PTC. LN stage was the only identified predictor of PTC recurrence.

The role of early 18F-FDG PET/CT in therapeutic management and ongoing risk stratification of high/intermediate-risk thyroid carcinoma

Little is known about the role in ongoing risk stratification of fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) performed early after radioactive iodine (RAI) ablation in differentiated thyroid carcinoma (DTC). The aim of the study is to investigate whether 18F-FDG PET/CT performed early after RAI ablation is useful to detect disease and to influence therapy and ongoing risk stratification. Patients with high/intermediate risk of recurrent DTC were included. 18F-FDG PET/CT scan was performed within 6 months after RAI ablation. We confirmed results with other imaging techniques, pathology reports, or follow-up. We classified the patient response as excellent, acceptable, or incomplete. Modified Hicks criteria were used to evaluate clinical impact. We included 81 patients with high/intermediate risk of recurrent DTC. Forty-one (50.6%) had positive uptake in 18F-FDG PET/CT, with negative (131)I whole-body scan ((131)I WBS). Sensitivity, specificity, and diagnostic accuracy of 18F-FDG PET/CT were 92.5, 90.2, and 91.4%, respectively. 18F-FDG PET/CT results had an impact on therapy in 38.3% of patients. One year after initial therapy, 45.7% showed excellent response, 8.6% acceptable response, and 45.7% incomplete response. A statistically significant relationship was found between negative 18F-FDG PET/CT and excellent response (80 vs. 12.2%, p < 0.001; OR 52.8). 18F-FDG PET/CT scan performed early in surveillance of patients with high/intermediate-risk thyroid carcinoma provides important additional information not available with conventional follow-up methods and had a high impact on therapy. A negative 18F-FDG PET/CT predicts an excellent response to therapy in the new ongoing risk stratification.

Correlative Studies in Clinical Trials: A Position Statement From the International Thyroid Oncology Group

OBJECTIVE

Patients with progressive thyroid cancer in distant metastatic sites represent a population with a need for new therapeutic options. Aspiring to improve the treatment of such patients, the objective of this position statement from the International Thyroid Oncology Group (ITOG) is to clarify the importance of incorporating high-quality correlative studies into clinical trials.

PARTICIPANTS

ITOG was formed to develop and support high-quality multicenter and multidisciplinary clinical trials for patients with aggressive forms of thyroid cancer. The Correlative Sciences Committee of the ITOG focuses on the quality and types of correlative studies included in ITOG-associated clinical trials.

EVIDENCE

This document represents expert consensus from ITOG regarding this issue based on extensive collective experience in clinical and translational trials informed by basic science.

CONSENSUS PROCESS

The Correlative Studies Committee identified an international writing group representative of diverse specialties, including basic sciences. Drafts were reviewed by all members of the writing group, the larger committee, and the ITOG board. After consideration of all comments by the writing group and modification of the document, the final document was then approved by the authors and the ITOG board.

CONCLUSIONS

High-quality correlative studies, which include variety in the types of correlates, should be intrinsic to the design of thyroid cancer clinical trials to offer the best opportunity for each study to advance treatment for patients with advanced and progressive thyroid cancer.

FDG PET performed at thyroid remnant ablation has a higher predictive value for long-term survival of high-risk patients with well-differentiated thyroid cancer than radioiodine uptake

PURPOSE

The predictive value of FDG PET at thyroid remnant ablation was evaluated in comparison to radioiodine uptake in high-risk patients with differentiated thyroid cancer.

PATIENTS AND METHODS

One hundred forty-one patients who underwent radioiodine therapy (RIT) after total thyroidectomy and received at least 1 further RIT due to suspected metastases were retrospectively analyzed. Patients had not received RIT previously. FDG PET was performed before thyroid remnant ablation. Thyroid-stimulating hormone-stimulated serum thyroglobulin (Tg) was measured for biochemical response assessment (change of Tg between the first and second RIT, ΔTg).

RESULTS

Biochemical response could be evaluated in 80 patients; survival data could be obtained for 88 patients (maximum, 124 months). Biochemical response was significantly better in patients with radioiodine-positive metastases compared with patients with radioiodine-negative metastases (median ΔTg I+, 55.8% vs I-, 112.6%; P < 0.01). Regarding survival, deaths occurred later in patients with radioiodine-positive metastases compared with radioiodine-negative patients; however, there was no significant difference regarding overall survival (I+, 61.3% vs I-, 58.2%; P > 0.05). Patients with FDG-positive metastases at thyroid remnant ablation showed a poorer biochemical response compared with patients with FDG-negative metastases (median ΔTg FDG+, 77.5% vs FDG-, 53.2%; P < 0.05), and these groups also differed significantly regarding survival (overall survival FDG+, 48.5% vs FDG-, 100%, P < 0.05).

CONCLUSIONS

At thyroid remnant ablation, FDG PET is more predictive for long-term survival, whereas radioiodine uptake is more important for short-term response. FDG PET performed at thyroid remnant ablation might represent a useful tool for management of high-risk patients with differentiated thyroid cancer.

Pretherapeutic dosimetry in patients affected by metastatic thyroid cancer using 124I PET/CT sequential scans for 131I treatment planning

PURPOSE

This study evaluates the use of sequential I PET/CT for predicting absorbed doses to metastatic lesions in patients with differentiated thyroid cancer undergoing I therapy.

METHODS

From July 2011 until July 2013, 30 patients with metastatic differentiated thyroid cancer were enrolled. Each participant underwent PET/CT at 4, 24, 48, and 72 hours with 74 MBq of I. Blood samples and whole-body exposure measurements were obtained to calculate blood and red marrow doses. Activity concentrations and lesion volumes obtained from PET/CT were used to evaluate tumor doses with medical internal radiation dose formalism and spheres modeling. Mean administered I therapeutic dose was 5994 MBq (range, 1953-11,455 MBq).

RESULTS

I PET/CT demonstrated all lesions detected by posttherapy I whole-body scans. Mean dose rates for blood, red marrow, and lesions were as follows: 0.07 ± 0.02 mGy/MBq, 0.05 ± 0.02 mGy/MBq, and 46.5 ± 117 mGy/MBq, respectively. Despite the high level of thyroid-stimulating hormone and CT detectable lesions, 15 of 30 patients did not show any abnormal I uptake.

CONCLUSIONS

The quantitative value of I PET/CT allows simple and accurate evaluation of lesion dosimetry following medical internal radiation dose formalism. Negative I PET/CT predicts absence of iodine avidity, potentially allowing avoidance of therapeutically ineffective I administration.

Prognostic role of 18F-FDG PET/CT in the postoperative evaluation of differentiated thyroid cancer patients

PURPOSE

The aim of this study was to evaluate the role of F-FDG PET/CT performed after surgery but before radioiodine therapy in patients with differentiated thyroid cancer.

PROCEDURES

FDG PET/CT was performed off l-thyroxine in 60 newly diagnosed differentiated thyroid cancer patients. Clinical and hematological evaluation as well as high-resolution neck ultrasound were performed. All patients underwent a complete follow-up (range, 6-67 months; mean [SD], 31.7 [20.6] months). The date of recurrence or the most recent office visit was recorded. Progression-free survival (PFS) is the primary end point of this study. Analysis was performed by Cox proportional hazards model. Survival curves were generated using Kaplan-Meier estimates, and the log-rank test was used to assess significance.

RESULTS

FDG PET/CT was negative in 63% of patients, 20% had FDG thyroid bed uptake, 5% distant metastases, and 12% lymph node FDG uptake. In patients with positive FDG PET/CT scan (ie, those with distant metastases or lymph node uptake), a higher rate of recurrence was observed (50% vs 6%, P < 0.05). Thyroglobulin, neck ultrasound, stage, and FDG PET/CT correlated with PFS at univariate analysis. At multivariate analysis, only thyroglobulin and FDG PET/CT continued to be predictors of PFS. Patients with a negative FDG PET/CT scan have a better PFS either in the whole group or in those with elevated thyroglobulin level (both >2 ng/mL and >10 ng/mL).

CONCLUSIONS

FDG PET/CT was abnormal in 17% of patients. Moreover, FDG PET/CT has an independent prognostic role, with a better PFS in patients with a negative scan.

Preablative Stimulated Thyroglobulin Levels Can Predict Malignant Potential and Therapeutic Responsiveness of Subcentimeter-Sized, 18F-fluorodeoxyglucose-Avid Cervical Lymph Nodes in Patients With Papillary Thyroid Cancer

PURPOSE

We investigated the potential value of TSH-stimulated serum thyroglobulin (sTg) to characterize subcentimeter-sized, F-FDG avid cervical lymph nodes (LNs) on 18PET/CT and their responsiveness to 131I ablation therapy (IAT) in patients with papillary thyroid cancer.

MATERIALS AND METHODS

We enrolled 49 patients who were undergoing total thyroidectomy and had incidentally detected FDG-avid LNs on PET/CT before IAT. According to the follow-up results, FDG-avid LNs were classified into 2 groups: those with metastatic LNs (group A) and those with benign LNs (group B). Differences in clinical and histopathologic variables at the time of IAT (e.g., age, sex, pT stage, pN stage, LN location, sTg level, TSH level, maxSUV, and size of each FDG-avid LN) were compared between groups, retrospectively. In addition, responsiveness to IAT was assessed by the intensity of iodine uptake in posttherapeutic 131I scans and by the reduction in LN size in follow-up studies.

RESULTS

Twenty of the 49 patients were classified in group A. By univariate analyses, sTg (P = 0.001), maxSUV of FDG-avid LN (P = 0.043), frequency of pT3-4 (P = 0.032), pN1b (P = 0.004), and FDG-avid LN located in mid to lower neck compartments (P = 0.011) were all significantly higher in group A than in group B. Among the 5 variables, the level of sTg was the only significant parameter that could predict metastatic LNs in multivariate analyses (OR, 1.86; 95% CI, 1.14-3.06; P = 0.014). An ROC curve showed that sTg level of 6.0 ng/mL was the optimal cutoff for predicting metastatic LNs (sensitivity, 95.0%; specificity, 93.1%; area under the curve, 0.971; SE, 0.0223). Interestingly, these metastatic LNs showed no significant uptake of 131I and no significant change of their size during follow-up.

CONCLUSIONS

Subcentimeter-sized FDG-avid LNs with high levels of sTg (>6.0 ng/mL) were metastatic, non-iodine avid and had little effect in IAT. Therefore, appropriate follow-up strategies need to be undertaken in these patients.

Postoperative fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography: an important imaging modality in patients with aggressive histology of differentiated thyroid cancer

BACKGROUND

Aggressive histopathologic subtypes of differentiated thyroid cancer (DTC) are fluorodeoxyglucose (FDG)-avid tumors and are at high risk for persistent/recurrent disease. In these patients, fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) is performed in cases of suspicion of recurrence based on thyroglobulin (Tg) levels or thyroglobulin antibodies (TgAb). The goals of this study were to evaluate the sensitivity of systematic postoperative FDG-PET/CT and to identify risk factors for abnormal FDG-PET/CT.

METHODS

Single-center retrospective study of 38 consecutive patients (16 males, 22 females; mean age, 57 years) with aggressive histology DTC, without known persistent disease at the time of postoperative radioactive iodine (RAI) ablation. The most frequent aggressive histologic subtypes were tall cell papillary carcinoma (45%) and poorly differentiated carcinoma (42%).

RESULTS

A total of 86 lesions were found in 20 (53%) patients, distributed in 33 organs. FDG-PET/CT and the postablation whole-body scan (RAI WBS) showed persistent disease in 15 and 12 patients, respectively. FDG-PET/CT was more sensitive than WBS for the detection of individual lesions (69% vs. 59%). Both imaging techniques were complementary with 41% of the lesions detected only by FDG-PET/CT and 31% only by RAI WBS. The only risk factor of abnormal FDG-PET/CT was a stimulated Tg level (Tg/TSH) measured at ablation >10 ng/mL with persistent disease showing FDG uptake in 72% of the patients with a Tg/TSH >10 ng/mL and in 10% of the patients with Tg/TSH ≤10 ng/mL.

CONCLUSION

Postoperative FDG-PET/CT should be performed routinely in patients with aggressive histology DTC.

Clinical significance of diffuse hepatic uptake on post-therapeutic early and delayed (131)I scan in differentiated thyroid cancer: a preliminary report

OBJECTIVE

The purpose of this study was to investigate the clinical significance of diffuse hepatic uptake on post-therapeutic early and delayed (131)I scan in patients with differentiated thyroid cancer (DTC).

METHODS

We retrospectively analyzed 219 DTC patients who underwent high-dose (131)I treatment and subsequent post-therapeutic dual (131)I scan. Both early (third day after (131)I treatment) and delayed (5-6th day after (131)I treatment) (131)I scan images were visually assessed and diffuse hepatic uptake was scored using a 4-point grading system depending on intensity.

RESULTS

On early (131)I scan, 73 patients (33.4 %) showed diffuse hepatic uptake, while 191 patients (87.2 %) patients showed diffuse hepatic uptake on delayed scan (p < 0.0001). The serum levels of ALT in patients with diffuse hepatic uptake on early scan were higher than those without diffuse hepatic uptake on early scan (p = 0.03 for ALT and p = 0.08 for AST). The serum levels of ALT and AST trended with the grade of hepatic uptake on delayed scan (p = 0.03 for ALT and p = 0.05 for AST). Diffuse hepatic uptake on early or delayed scan showed no significant relationship in the presence of thyroid remnants, metastatic DTC lesions, tumor recurrence during follow-up, and the serum thyroglobulin level (p > 0.05). On logistic regression analysis, both serum ALT (p = 0.01) and AST (p = 0.04) levels were significant predictive factors for diffuse hepatic uptake on early scan, while only serum ALT (p = 0.01) level was significant predictive factor for diffuse hepatic uptake on delayed scan.

CONCLUSIONS

The frequency of diffuse hepatic uptake on the delayed scan was significantly higher than the early scan. Diffuse hepatic uptake on early post-therapeutic scan and the intensity of diffuse hepatic uptake on delayed scan showed significant correlation with the serum levels of hepatic enzymes, but no significant association in the presence of thyroid remnants, metastatic DTC lesions, and tumor recurrence during follow-up. The timing and intensity of diffuse hepatic uptake on post-therapeutic scan may be related with factors such as hepatic function other than the thyroid tissue or DTC.

How to manage patients with differentiated thyroid cancer and a rising serum thyroglobulin level

Serum thyroglobulin (sTg) is the marker for monitoring persistence/recurrence of differentiated thyroid cancer, in patients without sTg antibodies. Patients with undetectable basal sTg or peak sTg <2 ng/mL are cured with low risk to recur. Newly detectable level of sTg indicates the recurrence. The significance of increasing sTg in patients treated with emithyroidectomy or total-thyroidectomy but not ablated with radioiodine is undefined. A doubling time <1 year may be a poor prognostic factor, but this is more relevant in cases with high levels of sTg. Because of its sensitivity, neck ultrasound should be performed at any visit, especially when an increased sTg is seen.