Detection of circulating Tg-mRNA in the follow-up of papillary and follicular thyroid cancer: how useful is it?

Assessment of the utility of measuring Thyroglobulin mRNA levels by Quantitative Real-Time PCR in the follow-up of differentiated thyroid cancer patients

INTRODUCTION

The determination of thyroglobulin levels by immunoassay and imaging studies is subject to interference by antithyroglobulin antibodies in up to 30% of cases, suggesting a need to find alternative methods for the follow-up of a significant number of thyroid cancer patients.

OBJECTIVES

Assess the sensitivity, specificity, and predictive values of thyroglobulin messenger RNA levels measured by quantitative Real Time-PCR (qRT-PCR) in the blood of patients followed for differentiated thyroid cancer.

METHODS

This is a prospective study of Tg-mRNA levels measured with qRT-PCR. A peripheral blood sample was taken in patients with excellent response (69) and with structural incomplete response to treatment (23). Results were analysed using the Unity Real-Time program and expressed as fg/μg RNA. A Receiver Operating Characteristic curve was constructed to assess Tg-mRNA cut-off values.

RESULTS

Tg-mRNA levels were not significantly different between the group with excellent response [0.10 fg/μg RNA (0.08-0.17)] and the group with incomplete structural response [0.133 fg/μg RNA (0.07-0.33)] (P < .06). Test sensitivity was 69.6%, specificity was 59.4%, negative predictive value was 85.4% and positive predictive value 36.4% CONCLUSIONS: Our experience shows that this technique could be useful as a rule-out test in selected cases, but its low sensitivity and specificity preclude its usefulness as a first-line test.

Assessment of the utility of measuring Thyroglobulin mRNA levels by Quantitative Real-Time PCR in the follow-up of differentiated thyroid cancer patients

INTRODUCTION

The determination of thyroglobulin (Tg) levels by immunoassay is subject to interference by antithyroglobulin antibodies in up to 30% of cases, suggesting a need to find alternative methods for the follow-up of a significant number of thyroid cancer patients.

OBJECTIVES

Assess the sensitivity, specificity, and predictive values of thyroglobulin messenger RNA (Tg-mRNA) levels measured by quantitative Real Time-PCR (qRT-PCR) in the blood of patients followed for differentiated thyroid cancer.

METHODS

This is a prospective study of Tg-mRNA levels measured with qRT-PCR. A peripheral blood sample was taken in patients with excellent response (n=69) and with structural incomplete response to treatment (n=23). Results were analysed using the Unity Real-Time program and expressed as fg/μg RNA. A Receiver Operating Characteristic curve was constructed to establish Tg-mRNA cut-off values.

RESULTS

Tg-mRNA levels were not significantly different between the group with excellent response [0.10fg/μg RNA (0.08-0.17)] and the group with incomplete structural response [0.133fg/μg RNA (0.07-0.33)] (p<0.06). Test sensitivity was 69.6%, specificity was 59.4%, negative predictive value was 85.4% and positive predictive value was 36.4%.

CONCLUSIONS

Our experience shows that this technique could be useful as a rule-out test in selected cases, but its low sensitivity and specificity preclude its usefulness as a first-line test.

Determining Specific Thyroid Transcripts in Peripheral Blood: A Single Center Study Experience

Thyroid carcinoma (TC) comprises a spectrum of different tumors with a wide range of biological behavior and prognosis. The techniques based on the latest trends in molecular biology may have application in diagnosis of metastatic TC. The aim of this study was to apply and analyze mRNA expression in peripheral blood of thyrotropin receptor [thyroid stimulating hormone receptor (TSHR-mRNA)] gene and thyroglobulin (Tg-mRNA) gene using 2^–ΔΔCt method in differentiated TC patients and healthy individuals. Fifty-seven subjects were included in the study, consisting of 40 patients with TC and 17 healthy volunteers as a control group. Total RNA was isolated from peripheral blood and used for two-step reverse transcriptase-polymerase chain reaction (PCR). Real-time PCR was performed with appropriate primers. Relative quantification using the 2^–ΔΔCt method was applied. Thyroid carcinoma patients with metastatic disease or loco-regional relapse expressed TSHR-mRNA by a 8.57-fold higher level than healthy controls. Thyroid carcinoma patients with biochemical relapse expressed TSHR-mRNA by a 14.17-fold higher level than healthy controls, while expression of Tg-mRNA was 6.6-fold higher in TC patients with metastatic disease and loco-regional relapse than healthy controls and 8.34-fold higher level compared with TC patients with excellent response to treatment. Our preliminary study showed that the TSHR gene expression might have more useful application as a biomarker compared to detection of Tg gene expression.

Circulating thyrotropin receptor messenger ribonucleic acid is not an effective marker in the follow-up of differentiated thyroid carcinoma

Background

Circulating thyrotropin receptor messenger ribonucleic acid (TSHR mRNA) assay has been validated in the follow-up of differentiated thyroid carcinoma (DTC) because of its high sensitivity during thyroid hormone therapy and no interference with endogenous anti-thyroglobulin antibodies (TgAb) compared to serum thyroglobulin (Tg). We investigated the efficacy of TSHR mRNA assay in 160 DTC patients using quantitative PCR (qPCR).

Findings

Only TSHR mRNA level of structural persistent disease with TgAb-positive (3.47 (2.97–9.53) pg equivalents/μg total RNA; p = 0.013) and its subgroup of distant metastasis patients with TgAb-positive (5.55 (3.28–12.52) pg equivalents/μg total RNA; p = 0.009) were significantly different from patients with no evidence of disease (2.32 (1.44–3.94) pg equivalents/μg total RNA). Applying cutoff at 2.00 pg equivalents/μg total RNA enabled us to predict structural persistent disease patients with a sensitivity of 62.3 % and a specificity of 42.9 %. Although, the sensitivity of TSHR mRNA assay in TgAb-postive patients (88.2 %) was superior than serum Tg (47.1 %) (p = 0.00002), the accuracy of the test is only 54.5 %.

Conclusions

This study demonstrated that TSHR mRNA assay has good sensitivity in TgAb-positive patients but it is neither specific enough as a first-line of testing nor a surrogate marker in the follow-up of our DTC patients.

Detection of thyroglobulin in antithyroglobulin antibody-positive sera by isoelectric focusing

Circulating antibodies have the potential to interfere with the measurement of thyroglobulin (Tg) in sera of patients. Here, we determined Tg concentration by isoelectric focusing (IEF) on agarose gel using for detection a rabbit antiserum to human Tg termed FLX. Tg was determined in sera of thyroid patients and HIV-infected patients under antiviral therapy. We showed that Tg IEF was not affected by the presence of anti-Tg antibodies (TgAb). Tg concentrations measured by IEF in TgAb-negative sera were in most of the cases, similar to those obtained by IRMA (immunoradiometric assay). However, in 5 of the 96 thyroid patients, and none of the 46 healthy subjects, Tg was undetectable by antiserum FLX and measurable by IRMA. In HIV-infected patients (64 men and 60 women), Tg was not recognized by FLX in 23 men and 9 women and this was related to abnormal CD4. We hypothesize that the decreased binding of FLX to Tg may be the result of conformational change on the Tg molecule, a phenomenon apparently related to immunodeficiency in HIV-infected patients. For thyroid patients, Tg IEF may be very useful for the interpretation of results when Tg measurements by IRMA and automated immunoassays are affected by interferences.

Thyroglobulin measurement by highly sensitive assays: focus on laboratory challenges

Differentiated thyroid cancer (DTC) is the most common endocrine cancer and its incidence has increased in recent decades. The initial treatment consists of total thyroidectomy followed by ablation of thyroid remnants by radioiodine in most cases. As thyroid cells are the only source of thyroglobulin (Tg), circulating Tg serves as a biochemical marker of persistent or recurrent disease in the follow-up of DTC. Due to the suboptimal clinical detection rate of older Tg assays endogenous or exogenous thyrotropin (TSH) stimulations are recommended for unmasking occult disease. However, the development of new Tg assays with improved analytical sensitivity and precision at low concentrations now allows detection of very low Tg concentrations, reflecting minimal amounts of thyroid tissue, even without the need for TSH stimulation. Even if the use of these assays still has not found its way in current clinical guidelines, such assays are now increasingly used in clinical practice. As serum Tg measurement is a technically challenging assay and criteria to define a ‘highly sensitive’ assay may be different, a good knowledge of the technical difficulties and interpretation criteria is of paramount importance for both clinical thyroidologists, laboratory physicians and scientists involved in the care of DTC patients.

Implications of thyroglobulin antibody positivity in patients with differentiated thyroid cancer: a clinical position statement

BACKGROUND

Even though the presence of antithyroglobulin antibodies (TgAbs) represents a significant problem in the follow-up of patients with differentiated thyroid cancer (DTC), the current guidelines on the management of DTC that have been published in recent years contain no text concerning the methods to be used for detecting such antibody-related interference in thyroglobulin (Tg) measurement or how to manage TgAb-positive patients in whom Tg cannot be used reliably as a tumor marker.

AIM

An international group of experts from the European Thyroid Association Cancer Research Network who are involved in the care of DTC patients met twice to form a consensus opinion on how to proceed with treatment and follow-up in TgAb-positive DTC patients based on the available evidence in the literature. Here we will report on the consensus opinions that were reached regarding technical and clinical issues.

RESULTS

This clinical opinion article provides an overview of the available evidence and the resulting consensus recommendations. The current literature does not provide sufficient data for giving evidence-based answers to many questions arising in the care of TgAb-positive DTC patients. Where insufficient evidence was available, a thorough discussion by a group of physician-scientists, all of whom have a distinguished track record in thyroid cancer care, was held to arrive at a consensus expert opinion. The questions and answers discussed were then summarized into an algorithm for the management of TgAb-positive patients.

CONCLUSION

We were able to define 26 consensus expert recommendations and a resulting algorithm for the care of TgAb-positive DTC patients.

Oncofetal fibronectin mRNA is highly abundant in the blood of patients with papillary thyroid carcinoma and correlates with high-serum thyroid-stimulating hormone levels

BACKGROUND

Papillary thyroid carcinoma (PTC) cells express oncofetal fibronectin (onfFN) mRNA, which may be useful to detect circulating tumor cells. The objective of this study was to determine the fraction of PTC patients having onfFN mRNA in their peripheral blood and to determine if onfFN mRNA levels are correlated with the status of the disease or with thyroid-stimulating hormone (TSH) serum concentrations.

METHODS

This study included 95 PTC patients, who were previously treated by thyroidectomy and radioactive iodine administration. Patients were examined by cervical sonography, whole-body (131)I scintigraphy, thyroglobulin measurement, and onfFN mRNA quantification both when they were being treated with L-thyroxine (L-T4) and after L-T4 withdrawal. The mean value for onfFN mRNA in blood from 25 healthy subjects was used as control for the onfFN mRNA assay.

RESULTS

After L-T4 withdrawal, serum TSH levels rose and onfFN mRNA was found in the peripheral blood of 33 of 64 (52%) disease-free patients, 15 of 23 (65%) patients with local residual disease, and 6 of 8 (75%) patients with known local or distant metastases. Continuous administration of L-T4 repressed serum TSH. In this state none of 17 (0%) disease-free patients and 1 of 4 (25%) patients with local residual disease had an elevated onfFN mRNA level, and 2 of 4 (50%) patients with metastasis had positive tests for serum onfFN mRNA.

CONCLUSIONS

onfFN transcripts are highly abundant in the peripheral blood of patients with PTC. L-T4 withdrawal, which produced elevated serum TSH concentrations in these athyroidic patients, markedly increased the fraction with positive tests for serum onfFN mRNA at all stages of the disease. Analyzing onfFN mRNA in the absence of a TSH stimulus allows a much better discrimination of different states of PTC disease and, based on current concepts of the significance of circulating mRNA, may be a useful tool to detect circulating thyroid cancer cells.

Current concepts and future directions in differentiated thyroid cancer

This paper provides an overview on the biology, monitoring and management of differentiated thyroid cancer (DTC), with particular attention to issues of relevance to clinical chemistry. The incidence of DTC appears to be increasing and management strategies are evolving as we learn more about its natural history and response to therapy. Clinical chemistry techniques play a central role in these protocols. Technical limitations inherent in current monitoring tools can hamper follow-up, although progress is being made. The molecular basis of DTC is being delineated with the potential to develop new strategies for diagnosis, monitoring and management of this condition.

Patients with differentiated thyroid cancer have a venous gradient in thyroglobulin levels

BACKGROUND

Although serum thyroglobulin (Tg) is an excellent marker for detecting recurrent or persistent differentiated thyroid cancer (DTC), it is unreliable in patients who have positive anti-Tg antibodies. Furthermore, a growing number of patients with DTC have elevated Tg levels but no detectable disease on radioiodine scanning or other imaging studies. The objective of this study was to determine whether a gradient in Tg protein level exists in patients with DTC.

METHODS

Fifteen patients who underwent thyroidectomy and/or lymph node dissection for primary DTC (n = 10 patients) and recurrent or persistent DTC (n = 5 patients). A venipuncture was performed simultaneously from the internal jugular vein adjacent to the tumor and the ipsilateral antecubital vein. Venous Tg protein levels were measured by using a chemiluminescence assay. RESULTS.: The average internal jugular-to-antecubital vein Tg protein ratio was 3.4:1.0 (median Tg ratio, 2.9:1; range, 0.8-62.2). Four patients had positive anti-Tg antibodies but still had a Tg gradient. Tg levels were significantly higher in the adjacent internal jugular vein than in the antecubital vein (P = .0019). The Tg ratio between the internal jugular and antecubital veins was significantly higher in patients with recurrent or persistent DTC than in patients with primary tumors (P = .0196).

CONCLUSIONS

To the authors' knowledge, this is the first study to document a venous gradient in Tg protein levels in patients with DTC. The findings suggested that venous sampling for Tg may be used to localize DTC in some patients who have high or increasing serum Tg levels but negative radioiodine scans or imaging studies.

Gene expression analysis and clinical diagnosis

BACKGROUND

A new basis for diagnostic tests is being provided by the vast amount of data on gene expression that are now becoming available through large-scale measurement of mRNA abundance. The insights gained from these resources are most likely going to provide both a better basic understanding of disease mechanisms, and to identify molecular markers for more precise diagnoses and for prediction of prognosis and treatment response.

METHODS

Some quantitative RT-PCR assays are utilized today for diagnosis of both malignant and non-malignant disease, but the use of gene expression measurements in clinical medicine can be expected to increase dramatically.

CONCLUSIONS

There are important technical issues that must be adequately solved in order to obtain robust assays, such as standardized protocols with appropriate quality controls that ensure reliable data for the specific samples being analysed and good inter-laboratory reproducibility.

Oncofoetal fibronectin--a tumour-specific marker in detecting minimal residual disease in differentiated thyroid carcinoma

Supposedly, thyrocyte-specific transcripts such as thyroglobulin (Tg) and thyroid-stimulating hormone receptor (TSH-R) were proposed to be useful for the diagnosis of circulating tumour cells in patients suffering from differentiated thyroid carcinoma (DTC). However, several research groups reported blood-borne Tg transcripts in healthy individuals. This study determines in particular the origin of Tg mRNA in nucleated blood cells and analyses whether other tumour-associated sequences are absent in leukocytes, but widely expressed in DTC. Therefore, expression analyses for Tg, TSH-R, cytokeratin 19 (CK 19), human telomerase reverse transcriptase (hTERT) and oncofoetal fibronectin (onfFN) were carried out using cDNAs derived from (1) leukocyte fractions, (2) 18 follicular thyroid carcinomas (FTCs) and 48 papillary thyroid carcinomas (PTCs), and (3) leukocytes of two thyrocyte-depleted individuals treated for C-cell carcinoma of the thyroid. Expression of onfFN was additionally analysed by semiquantitative RT–PCR and by quantitative fluorescence-based real-time PCR. Tg and TSH-R expression was demonstrated not only in both athyroid individuals, but in all leukocyte subgroups tested, while hTERT was absent in resting CD4⁺ cells and only weakly expressed in the CD8⁺ group. CK 19 was notable in each leukocyte population except for resting CD14⁺, as well as for activated and resting CD19⁺ cells. All blood cell fractions proved negative for onfFN mRNA, whereas its presence in thyroid carcinoma was 78/98% (FTC/PTC). Threshold cycle values were calculated at: porphobilinogen deaminase (PBGD) =25.95±0.73 (FTC)/24.55±5.43 (PTC) (P=0.2878); onfFN=25.48±3.15 (FTC)/21.44±3.44 (PTC) (^*P=0.0001). Finally, onfFN transcripts were detected in blood samples of six out of nine patients with known DTC metastases, demonstrating a reliable assay functionality. We propose that real-time RT–PCR of onfFN mRNA is superior to other markers in monitoring minimal residual disease in DTC with regard to both assay sensitivity and specificity.