Circulating thyroglobulin transcytosed by thyroid cells in complexed with secretory components of its endocytic receptor megalin

After its endocytosis from the colloid, some thyroglobulin (Tg) is transcytosed intact across thyrocytes, accounting in part for its presence in the circulation. We previously showed that megalin (gp330), an endocytic Tg receptor, mediates apical to basolateral Tg transcytosis. Here we investigated whether a portion of megalin remains combined with Tg after its transcytosis, using studies with cultured thyroid cells and in vivo observations. FRTL-5 cells, a rat thyroid cell line, cultured on filters in dual chambers form tight junctions and exhibit features of polarity, with expression of megalin exclusively on the upper (apical) surface. After the addition of unlabeled Tg to the upper chamber and incubation at 37 C, some Tg was transcytosed intact across FRTL-5 cells into the lower chamber. Two antimegalin ectodomain antibodies precipitated transcytosed Tg in fluids collected from the lower chamber. After the addition of Tg to surface-biotinylated FRTL-5 cells, an anti-Tg antibody and the two antimegalin ectodomain antibodies precipitated high molecular mass biotinylated material in fluids collected from the lower chamber, corresponding to much of the megalin ectodomain, as well as smaller amounts of lower molecular mass material. The results indicate that Tg transcytosed across FRTL-5 cells remains complexed with megalin ectodomain components, which we refer to as megalin secretory components. In aminotriazole-treated rats, which develop increased megalin-mediated Tg transcytosis, antimegalin antibodies precipitated some of the Tg in the serum. Tg was also precipitated by antimegalin antibodies in sera from patients with Graves' disease, in which we found increased megalin expression on the apical surface of thyrocytes. In contrast, in thyroidectomized patients with metastatic papillary thyroid carcinoma, in whom Tg is directly secreted by neoplastic thyroid cells into the circulation rather than transcytosed, serum Tg was not precipitated by antimegalin antibodies. The detection of Tg-megalin complexes may help identify the source of serum Tg in patients with thyroid diseases.     

Diagnosis of metastases in patients with papillary thyroid cancer by the measurement of thyroglobulin in fine needle aspirate

The widespread use of neck ultrasonography (US) during the follow-up of patients with papillary thyroid carcinoma (PTC) has led to the discovery of small cervical lymph nodes (LN). Although US has a high sensitivity for diagnosing LN, fine needle aspiration biopsy (FNA) and measurement of thyroglobulin in fine needle aspirates (FNA-Tg) have proven to be invaluable tools. The aim of this study is to determine the sensitivity of the combined use of neck US, FNA biopsy and FNA-Tg for diagnosis of cervical lymph nodes. We have studied 32 patients with 44 LN detected by US, 19 classified as inflammatory and 25 as suspicious. 15 of those 25 suspicious LN had high FNA-Tg (13 of the 15 had positive cytology and 2 indeterminate). All of these 15 LN (11 patients) were proven to be PTC metastasis by histopathology. All 19 inflammatory LN and those 10/25 suspicious LN, had cytology negative for malignancy and undetectable FNA-Tg. We conclude that fine needle aspiration biopsy and FNA-Tg combined with neck US are essential for detecting positive cervical lymph nodes due to its high sensitivity and specificity and it should be considered the standard for investigating locally recurrent disease in patients with PTC.     

Presurgical serum thyroglobulin has no prognostic value in papillary thyroid cancer.

We investigated whether serum thyroglobulin determination before surgery for differentiated thyroid carcinoma may have any prognostic value with regard to tumour extension and disease outcome in a retrospective series of 71 patients with papillary thyroid cancer. Presurgical serum thyroglobulin levels were correlated with the size of the primary tumoral nodule (p = 0.006) and of the whole thyroid (p = 0.02). The same correlation was found in a control group of patients with benign thyroid nodules, confirming that presurgical serum thyroglobulin cannot be used for the differential diagnosis of thyroid carcinoma. Presurgical serum thyroglobulin levels did not differ among patients with tumor limited to thyroid gland or extending to cervical lymph nodes or invading outside the thyroid capsule or metastasising to distant size. In addition presurgical serum thyroglobulin levels were not correlated with the disease outcome after a mean follow-up of 9 years: no difference was found among patients in complete remission or with persistent disease or dead from thyroid cancer. In conclusion, this study failed to show any prognostic value of presurgical serum thyroglobulin determination that consequently should not be measured.     

Comparison of seven serum thyroglobulin assays in the follow-up of papillary and follicular thyroid cancer patients

BACKGROUND: Serum thyroglobulin (Tg) is the marker of differentiated thyroid cancer after initial treatment and TSH stimulation increases its sensitivity for the diagnosis of recurrent disease. AIM: The goal of the study is to compare the diagnostic values of seven methods for serum Tg measurement for detecting recurrent disease both during L-T4 treatment and after TSH stimulation. METHODS: Thyroid cancer patients who had no evidence of persistent disease after initial treatment (total thyroidectomy and radioiodine ablation) were studied at 3 months on L-T4 treatment (Tg1) and then at 9-12 months after withdrawal or recombinant human TSH stimulation (Tg2). Sera with anti-Tg antibodies or with an abnormal recovery test result were excluded from Tg analysis with the corresponding assay. The results of serum Tg determination were compared to the clinical status of the patient at the end of follow-up. RESULTS: Thirty recurrences were detected among 944 patients. A control 131I total body scan had a low sensitivity, a low specificity, and a low clinical impact. Assuming a common cutoff for all Tg assays at 0.9 ng/ml, sensitivity ranged from 19-40% and 68-76% and specificity ranged from 92-97% and 81-91% for Tg 1 and Tg2, respectively. Using assays with a functional sensitivity at 0.2-0.3 ng/ml, sensitivity was 54-63% and specificity was 89% for Tg1. Using the two methods with a lowest functional sensitivity at 0.02 and 0.11 ng/ml resulted in a higher sensitivity for Tg1 (81% and 78%), but at the expense of a loss of specificity (42% and 63%); finally, for these two methods, using an optimized functional sensitivity according to receiver operating characteristic curves at 0.22 and 0.27 ng/ml resulted in a sensitivity at 65% and specificity at 85-87% for Tg1. CONCLUSION: Using an assay with a lower functional sensitivity may give an earlier indication of the presence of Tg in the serum on L-T4 treatment and may be used to study the trend in serum Tg without performing any TSH stimulation. Serum Tg determination obtained after TSH stimulation still permits a more reliable assessment of cure and patient's reassurance.     

A single recombinant human thyrotropin-stimulated serum thyroglobulin measurement predicts differentiated thyroid carcinoma metastases three to five years later

CONTEXT: Testing for residual differentiated thyroid carcinoma relies heavily upon recombinant human (rh)TSH-stimulated serum thyroglobulin (Tg) levels, but the positive predictive value is often low. OBJECTIVE: Our objective was to determine the accuracy of a single rhTSH-Tg measurement over time. DESIGN AND SETTING: We conducted a prospective follow-up study at the University referral center. PATIENTS: A total of 107 differentiated thyroid carcinoma patients were stratified according to their initial rhTSH-Tg as follows: group 1 with Tg less than 0.5 (n = 68), group 2 with Tg of 0.6-2.0 (n = 19), and group 3 with Tg greater than 2 ng/ml (n = 20). INTERVENTION: Clinical evaluations were conducted over 0.9-5.2 yr as follows: Tg during thyroid hormone suppression (n = 27), after rhTSH (n = 59), and/or after thyroid hormone withdrawal (n = 15). MAIN OUTCOME: Tumor was identified in one patient in each of groups 1 (1.6%) and 2 (5.5%), and 16 in group 3 (80%), comprising 19 tumor locations: 11 locoregional, two mediastinal, five lung, and one brain. Tumor was found in 81% with an initial or follow-up rhTSH-Tg greater than 2 ng/ml. TSH-stimulated Tg fell spontaneously to less than 0.5 ng/ml in 50% of group 2 and 5% of group 3 over 1.7-5.0 yr. The positive predictive value of the initial rhTSH-Tg greater than 2 ng/ml was 80%, and the negative predictive value was 98%. After retreatment, 100% of group 1, 74% of group 2, and 55% of group 3 had no evidence of tumor (P = 0.0001). CONCLUSIONS: 1) A single rhTSH-Tg greater than 2 ng/ml predicts persistent tumor, although no value entirely excludes future recurrence. 2) Repeated TSH-stimulated studies are appropriate for patients at risk of recurrence, especially those with an rhTSH-Tg greater than 1 ng/ml. 3) A single rhTSH-Tg less than 0.5 ng/ml without Tg antibody has an approximately 98% likelihood of identifying patients completely free of tumor, a large group in which TSH suppression to less than 0.1 mIU/liter and frequent imaging and TSH-stimulated Tg testing are unnecessary.     

A consensus report of the role of serum thyroglobulin as a monitoring method for low-risk patients with papillary thyroid carcinoma

Recent studies have provided new information regarding the optimal surveillance protocols for low-risk patients with differentiated thyroid cancer (DTC). This article summarizes the main issues brought out in a consensus conference of thyroid cancer specialists who analyzed and discussed this new data. There is growing recognition of the value of serum thyroglobulin (Tg) as part of routine surveillance. An undetectable serum Tg measured during thyroid hormone suppression of TSH (THST) is often misleading. Eight studies show that 21% of 784 patients who had no clinical evidence of tumor with baseline serum Tg levels usually below 1 micro g/liter during THST had, in response to recombinant human TSH (rhTSH), a rise in serum Tg to more than 2 micro g/liter. When this happened, 36% of the patients were found to have metastases (36% at distant sites) that were identified in 91% by an rhTSH-stimulated Tg above 2 micro g/liter. Diagnostic whole body scanning, after either rhTSH or thyroid hormone withdrawal, identified only 19% of the cases of metastases. Ten studies comprising 1599 patients demonstrate that a TSH-stimulated Tg test using a Tg cutoff of 2 micro g/liter (either after thyroid hormone withdrawal or 72 h after rhTSH) is sufficiently sensitive to be used as the principal test in the follow-up management of low-risk patients with DTC and that the routine use of diagnostic whole body scanning in follow-up should be discouraged. On the basis of the foregoing, we propose a surveillance guideline using TSH-stimulated Tg levels for patients who have undergone total or near-total thyroidectomy and (131)I ablation for DTC and have no clinical evidence of residual tumor with a serum Tg below 1 micro g/liter during THST.     

Usefulness of thyroglobulin measurement in needle washouts of fine-needle aspiration biopsy for the diagnosis of cervical lymph node metastases from papillary thyroid cancer before thyroidectomy

In evaluating cervical lymph node (LN) metastasis from papillary thyroid cancer (PTC), ultrasonography (US)-guided fine-needle aspiration biopsy (FNAB) is very important tool. There were limited number of studies about the diagnostic value of thyroglubion measurement in FNAB (FNAB-Tg) in non-thyroidectomized patients. Therefore, in this study, the authors evaluated the role of FNAB-Tg in diagnosing cervical LN metastases in patients with PTC before thyroidectomy. A total 91 suspicious LNs of 68 patients were undergone US-guided FNAB-Tg and cytology. Any FNAB-Tg concentration above 50?ng/ml considered as positive, irrespective of thyroid gland presence. Based on the final pathology, 49 LNs were positive, and the remaining 42 LNs were negative for metastasis. The sensitivity, specificity, and accuracy of FNAB-Tg in thyroidectomized patients were 80.0, 100.0, and 88.9%, respectively. The diagnostic performance of FNAB-Tg was not compromised by the presence of thyroid gland (sensitivity, specificity and accuracy?=?95.0, 90.9 and 93.2%, respectively). FNAB-Tg is useful and simple method for the diagnosis of metastatic cervical LNs from PTC. The diagnostic performance of FNAB-Tg was not compromised by the presence of thyroid gland. Therefore, FNAB-Tg could be performed actively for the LN staging of PTC.     

Approach to the patient with a positive serum thyroglobulin and a negative radioiodine scan after initial therapy for differentiated thyroid cancer

The 10-yr survival of differentiated thyroid cancer is about 76-93%, and at least 10% of patients manifest tumor persistence or recurrence, depending on their disease stage, after initial therapy, which typically includes total thyroidectomy and (131)I ablation. Previously the realization of their residual/recurrent cancer often presented simultaneously with the additional surprise that they lacked pathological uptake on their diagnostic whole-body radioiodine image despite their elevated stimulated serum thyroglobulin (Tg) level, a scenario referred to as the scan-negative, Tg-positive patient. Now that serum Tg and neck ultrasonography have supplanted the diagnostic whole-body scan because of its inferior sensitivity, patients are often recognized to harbor residual disease without radioiodine imaging, and a new challenging scenario has emerged: the ultrasonography-negative, Tg-positive patient. Similarities and differences of these two patient populations aside, these Tg-positive patients are frequently encountered, and some are considered for additional (131)I therapy, although now typically after negative anatomic +/- (18)F-fluorodeoxyglucose positron emission tomography imaging or in the setting of known or suspected distant metastases already localized by anatomic imaging. Thus, the scan-negative, Tg-positive patient of today differs from those of the past, but the term still has relevance to current practice. The optimal evaluation and treatment of these patients remain controversial, partly because many of these patients will not die from thyroid cancer, and there are no randomized trials to demonstrate that intervention could have prevented the deaths that do occur. Here a case is presented that adds the complexity of advanced age, and one approach to these challenging patients is offered.     

Serum thyroglobulin levels after thyroxine withdrawal in patients with low risk papillary thyroid carcinoma.

We hypothesized that elevated levels of serum thyroglobulin (Tg) are frequently found as the only index of residual neoplasm in patients with low-risk papillary thyroid carcinoma. The records of patients operated on for papillary thyroid carcinoma over a 2-year period were reviewed, and the patients were allocated to risk groups by a validated staging method that does not include Tg levels. Of the 35 patients who manifested a low-risk carcinoma, 9 (26%) exhibited elevated Tg concentrations (11-53 ng/mL) during thyroxine withdrawal after therapies, while clinical, scintigraphic, and radiographic studies at least 1 year later showed no evidence of tumor. Prior scintigraphic imaging of therapeutic doses of 131I in 8 of 9 patients demonstrated no distant metastases, further confirming the low-risk status of this group. The staging method predicts that only 0.9% of patients with low-risk papillary carcinoma will have a cause specific death in 20 years. Elevated Tg concentrations have not been shown to forecast independently the survival of patients with low-risk papillary carcinoma. Thus, although frequently encountered, elevated Tg concentrations are unlikely to predict shortened survival in patients with papillary carcinoma for whom low risk has been determined from other data.     

Prognostic value of serial serum thyroglobulin determinations after total thyroidectomy for differentiated thyroid cancer

Serial weekly serum samples (for 3 weeks) were obtained from 42 patients with differentiated thyroid cancer (DTC, papillary no.=35, follicular no.=6, Hurthle cell no.=1) for serum thyroid hormone, TSH and TG before and after total thyroidectomy. Serum specimens were also obtained one month after radioiodine (131I) therapy followed by suppressive dose of L-thyroxine (L-T4, 2.5 microg/kg). The patients were subdivided into four groups: group I: the DTC was confined to a single solid nodule (no.=1 2); group II: thyroid malignancy invaded local cervical structures but there were no lymph node metastases (no.=8); group III: DTC with lymph node metastases (no.=6); and group IV: DTC with distant metastases (no.=16). In all group I patients serum TG remained undetectable in spite of elevated serum TSH levels at the 3rd week post-surgery (PS). Only one of group II patients had a detectable serum TG value of 5.2 ng/ml (3rd week PS). By contrast, 37.5% of group III patients had detectable serum TG levels, ranging from 3.4 to 16.8 ng/ml (3rd week PS). Lymph node metastases were detected in 5 of these patients by whole body scan (WBS) and removed surgically in 3. As expected, group IV patients had elevated serum TG values ranging 33.0-958.0 ng/ml and distant metastases were confirmed in all of them by WBS. From the calculations through univariate logistic regression comparing TG concentrations at the 3rd week PS from groups I and II vs groups III and IV, we obtained a cut-off value of 2.3 ng/ml with the following efficacy features: sensitivity=74.5%; specificity=95%; positive predictive value=92.3%; negative predictive value=65.5%; and accuracy=73.8%. After 131I and L-T4 suppressive therapy, only 5 out of 36 patients of groups I, II and III had detectable serum TG levels (3.1-7.0 ng/ml) whereas serum TG was detectable in all group IV patients (ranging 2.5-8.6 ng/ml). We concluded that serum TG concentrations above 2.3 ng/ml at the 3rd week PS could be suggestive of lymph node or distant metastases in patients with DTC. Patients with serum TG above this limit could be considered at risk for metastatic disease and higher doses of diagnostic iodine-131 (131I) may be indicated for actinic ablation.     

Evaluation of the diagnostic value of the first thyroglobulin determination in detecting metastases after differentiated thyroid carcinoma surgery.

AIM: Evaluation of the diagnostic value of the first thyroglobulin (Tg) level measurement, performed after thyroidectomy, before another treatment, as an early marker of either metastases or local recurrence of differentiated thyroid carcinoma (DTC). MATERIALS AND METHODS: Data of 178 patients (160 women, 18 men, 14-79 years) with DTC and without known interference in Tg assay were evaluated retrospectively. In all patients, neck radioiodine uptake (Tup (24)), thyroid remnants volume (V), TSH and Tg were measured. The Tg/V and Tg/Tup (24) ratios were calculated to correct Tg concentration with regard to V and Tup (24). Six months after initial evaluation and routine therapy all patients underwent control examinations under endogenous TSH stimulation. RESULTS: During follow-up metastases or local recurrence were found in 32 patients. The groups of patients with no diagnosed metastases (M0) and with detected metastases (M1), did not differ with regard to V, serum TSH or Tup (24); difference between the two groups was found in Tg concentration (4.3 ng/ml VS 97.4 ng/ml; p=0.000001). The ratios of Tg/Tup (24) (p=0.000000) and Tg/V (p=0.004) were lower in the group M0 than M1. The areas under receiver operating characteristic curves (ROC) for Tg concentrations, Tg/Tup (24), and Tg/V ratios were 0.773 (95% CI - 0.655-0.892), 0.817 (0.709-0.925) and 0.712 (0.541-0.884), respectively. CONCLUSIONS: Both the absolute Tg concentration and Tg/V and Tg/Tup (24) ratios, determined after thyroidectomy but before another treatment in patients with metastases of DTC, diagnosed within 6 months after (131)I administration, are higher than those in patients without such metastases. This indicates that the mentioned parameters may be applied as early markers of either local recurrence or metastases of DTC. The highest discriminative value demonstrates Tg/Tup (24) ratio, Tg concentration has a lower value and Tg/V ratio has the lowest one.     

Relationship between tumor burden and serum thyroglobulin level in patients with papillary and follicular thyroid carcinoma.

Serum thyroglobulin (Tg) is a reliable marker for detecting recurrent and persistent disease during the follow-up of patients with papillary and follicular thyroid carcinoma. The goal of this study was to assess the relationship between the serum Tg level measured after thyroid hormone withdrawal and the tumor mass in thyroid cancer patients who underwent surgery with the use of an intraoperative probe for lymph node metastases with (131)I uptake. Patients were classified into one of three groups according to the Tg level: undetectable (n = 18); 1-10 ng/mL (n = 21); and greater than 10 ng/mL (n = 33). The main clinical characteristics and the extent of the disease at the time of initial treatment were similar in these three groups. Lymph node metastases were found in 13 of the 18 patients with undetectable Tg level. Eight patients had persistent foci of uptake after surgery that were located behind the sterno-clavicular joint in six patients. The number of metastatic lymph nodes and their total surface (in mm(2)) or their total volume (in mm(3)) were significantly linked with serum Tg/thyrotropin [TSH] level (p = 0.002 and p < 0.0001, respectively). For a given metastatic surface or volume, the serum Tg/TSH value was no longer linked with the number of metastatic lymph nodes (p = 0.32), suggesting that the total surface or total volume is the characteristic that best summarizes the influence of the disease on the serum Tg/TSH level. In conclusion, patients with higher serum Tg levels tend to have more extensive disease and should undergo more aggressive treatment modalities. Nevertheless, undetectable serum Tg should not be considered as a reliable criteria to exclude a minimal tumor burden in patients who have already been treated with (131)I.     

Identification of thyroid hormone residues on serum thyroglobulin: a clue to the source of circulating thyroglobulin in thyroid diseases

Thyroglobulin (Tg) present in the serum of normal individuals and patients with thyroid disorders could be partly newly synthesized non-iodinated Tg and partly Tg containing iodine and hormone residues originating from the lumen of thyroid follicles. With the aim of examining the contribution of the latter source of Tg to the elevation of serum Tg concentration in thyroid pathophysiological situations, we devised a procedure to identify thyroxine (T4) and tri-iodothyronine (T3) residues on Tg from unfractionated serum. A two-step method, basedon (i)adsorption of Tg on an immobilized anti-human Tg (hTg) monoclonal antibody (mAb) and (ii)recognition of hormone residues on adsorbed Tg by binding of radioiodinated anti-T4 mAb and anti-T3 mAb, was used to analyze serum Tg from patients with either Graves' disease (GD), subacute thyroiditis (ST) or metastatic differentiated thyroid cancer (DTC). Purified hTg preparations with different iodine and hormone contents were used as reference. Adsorption of purified Tg and serum Tg on immobilized anti-hTg mAb ranged between 85 and 90% over a wide concentration range. Labeled anti-T4 and anti-T3 mAbs bound to adsorbed purified Tg in amounts related to its iodine content. Tg adsorbed from six out of six sera from ST exhibited anti-T4 and anti-T3 mAb binding activities. In contrast, significant mAb binding was only observed in one out of eight sera from untreated GD patients and in 1 out of 13 sera from patients with DTC. The patient with DTC, whose serum Tg contained T4 and T3, represented a case of hyperthyroidism caused by a metastatic follicular carcinoma. In conclusion, we have identified, for the first time, T4 and T3 residues on circulating Tg. The presence of Tg with hormone residues in serum is occasional in GD and DTC but is a common and probably distinctive feature of ST.     

临诊应对:如何处理经初次治疗后血清甲状腺球蛋白阳性而放射性碘扫描阴性的分化型甲状腺癌患者

分化型甲状腺癌的初次治疗通常使用甲状腺全切除术和131I照射,患者10年牛存率约为76%～93%,至少10%术后有癌组织残留或肿瘤复发,与治前的疾病分期有关.以前即发现这些患者在甲状腺癌残留/复发时.     

Management of low-risk well-differentiated thyroid cancer based only on thyroglobulin measurement after recombinant human thyrotropin.

A multicenter study was undertaken to ascertain prevalence and significance of recombinant human thyrotropin (rhTSH)-stimulated increases in thyroglobulin (Tg) levels in thyroid cancer patients classified to be at low risk for recurrence. Patients were eligible for enrollment if they had undergone near-total or total thyroidectomy and remnant ablation between 1-10 years prior to enrollment and had received thyroxine suppression therapy (THST) with a TSH level of < 0.5 mU/L and Tg level less than or equal to 5 ng/mL within the prior year. Patients with anti-Tg antibodies, distant metastases, or other evidence of residual disease were excluded. Four hundred eighty-six patients were entered into the study, and 300 were considered eligible and comprise the study population. TSH, Tg, and anti-Tg antibody levels were obtained at baseline, followed by intramuscular injection of 0.9 mg of rhTSH on days 1 and 2 and measurement of Tg on day 5. After rhTSH, 53 patients (18%) had elevations in Tg of at least 2 ng/mL, including 33 patients (11%) with increases from baseline of equal to or greater than 5 ng/mL. Patients with an initial advanced stage of disease were more likely to display elevations in Tg after rhTSH. One third of those with stage III disease displayed elevations in Tg of 2 ng/mL or more. Patients within 5 years of thyroidectomy were as likely to display elevations in rhTSH-stimulated Tg as those 5-10 years from surgery. In conclusion, these data suggest rhTSH-stimulated Tg testing without scan may be a useful tool in the follow-up of patients with low-risk thyroid cancer, and may serve to identify patients previously thought free of disease on the basis of undetectable Tg levels while undergoing THST. A strategy is presented for incorporation of this approach into the management of patients with low-risk well-differentiated thyroid cancer.