Serum thyroglobulin measurements in differentiated thyroid cancer

Routine thyroglobulin, neck ultrasound and physical examination in the routine follow up of patients with differentiated thyroid cancer-Where is the evidence?

PURPOSE

Patients with differentiated thyroid cancer (DTC) typically have a favourable prognosis and recurrence as late as 45 years after diagnosis has been reported. International clinical guidelines for monitoring recommend routine thyroglobulin, ultrasound and physical examination for the detection of recurrence. The aim of this review was to systematically review whether routine monitoring using thyroglobulin (Tg), neck ultrasound and physical examination for recurrence in differentiated thyroid cancer patients is effective in improving patient survival and/or quality of life.

METHODS

Primary studies were retrieved via a comprehensive search of three electronic bibliographic databases (PubMed, Web of Science Core Collection and Cochrane Library) without time restriction. Eligible studies must have reported on disease-free patients with DTC subject to long-term routine surveillance. The primary and secondary outcomes of interest were overall survival (or other survival parameters) and quality of life, respectively.

RESULTS

Literature searches yielded 5529 citations, which were screened by two reviewers. 241 full texts were retrieved. No randomised controlled trials or two-arm cohort studies on the effectiveness of any of the three specified interventions were identified. However, three 'single-arm' studies reporting long-term follow-up outcomes in patients undergoing regular surveillance were identified and appraised.

CONCLUSIONS

This review highlights a lack of empirical evidence to support current use of routine surveillance in DTC. Although early detection is possible, routine surveillance may lead to unnecessary intervention.

[Thyroglobulin mRNA amplification in peripheral blood of patients with differentiated thyroid carcinoma: what does it really mean?]

Despite the excellent prognosis, differentiated thyroid carcinoma (DTC) may recur in 20-40%, and prognosis is particularly related to early detection of recurrent disease. Therefore, long-term follow-up with sensitive tests is need. Serum thyroglobulin (Tg) has an established role as a tumor marker of relapse. However, there are technical limitations of Tg immunoassays, in special, the interference of anti-Tg antibodies and the method sensitivity is dependent on TSH stimulation. Detection of circulating malignant cells by amplification of tumor-specific mRNA showed initial promising results. However, almost one decade of studies of Tg mRNA detection in peripheral blood, its real contribution for DTC follow-up had not yet been established. After a critical analysis of published data, it is clear that there are many protocol differences and conflicting results. Therefore, it seems that amplification of thyroid-specific mRNAs is not superior to sensitive Tg assays and illegitimate transcription and alternative splicing of Tg are factors that may influence mRNA test specificity.

Serum thyroglobulin measurement: clinical background and main methodological aspects with clinical impact

It is worldwide recognized that circulating thyroglobulin (Tg) measurement represents a fundamental tool in the follow-up of patients affected by differentiated thyroid cancer (DTC). In the last American and European Consensus Conferences, a surveillance guideline has been extended to the use of thyrotropin (TSH)-stimulated Tg levels for thyroidectomized patients without clinical evidence of residual tumor with Tg below 1 microg/l during TSH suppression. Therefore, sensitivity of the methods is critical to detect small amounts of Tg and/or to observe minimal changes in Tg concentration in the management of DTC patients. It has been proposed that only methods providing the greatest distinction between the lower limit of euthyroid reference range (approximately 3.0 microg/l) and the functional sensitivity limit (at least 1 microg/l) of the assay may offer a suitable clinical sensitivity for detecting small amounts of functioning thyroid tissue in TSH-suppressed state (1 g of normal thyroid tissue results in a serum Tg of approximately 1 microg/l when TSH is normal and about 0.5 microg/l when TSH is suppressed). In the last 30 years sensitivity of Tg measurements has been greatly improved, nowadays methods can achieve very good analytical and functional sensitivity to give reliable results also in the very low concentration range (between 0.1 and 1 microg/l). In addition, with the introduction of fully automated assays, results can be readily available to the clinician while patients are still in the ambulatory area. However, despite the large clinical use of Tg measurement, wide differences (by threefold) still remain between results produced in different laboratories due to poor standardization, heterogeneity of circulating Tg, interference from auto-antibodies, differences in the epitope recognition by antibodies used in the assays.

Thyroid nodules: Does the suspicion for malignancy really justify the increased thyroidectomy rates?

Thyroid nodules are frequently diagnosed today, mainly due to the wide use of neck ultrasonography (US). The majority of these are benign; suspicion for malignancy is an indication for surgery, while benign thyroid nodules may be managed conservatively. There is evidence that a large percentage of patients with thyroid nodules (many diagnosed incidentally) are over-treated. Careful and accurate identification of patients with thyroid nodules highly suspicious for underlying malignancy would allow a more reasonable therapeutic approach and would result in a reduction of the number of unnecessary thyroidectomies. Fine-needle aspiration cytology (FNAC), in conjunction with high-resolution thyroid US, are currently the most accurate and cost-effective diagnostic approach for the evaluation of patients with nodular thyroid disease. Radionuclide thyroid scanning should be used selectively. By increasing the use of FNAC, it is expected that the number of unnecessary thyroidectomies will be further diminished, thereby avoiding over-treatment, without exposing the patients to the risk of under-treatment for a highly curable cancer. However, accurate preoperative diagnosis of thyroid cancer within a thyroid nodule is not always possible and, although the problem of unnecessary surgery can further be diminished, it cannot be completely eliminated.

High-sensitivity human thyroglobulin (hTG) immunoradiometric assay in the follow-up of patients with differentiated thyroid cancer

Circulating human thyroglobulin (hTG) measurement has a pivotal role in the management of patients affected by differentiated thyroid cancer (DTC). Generally, hTG serum concentration less than 1 ng/ml is considered a marker of complete remission after total thyroid ablation. Recently, high-sensitivity immunoradiometric assays (IRMA) have been developed to detect very low hTG serum concentrations. The present study was undertaken to test a newly developed high-sensitivity hTG IRMA and to evaluate its diagnostic performance and reproducibility in the follow-up of patients affected by DTC. We retrospectively selected 156 patients without signs of recurrence and 39 patients with DTC recurrence. Serum samples were collected during L-thyroxine (T4) suppressive therapy (ONT4) and 4 weeks after T4 withdrawal (OFFT4), and hTG was measured by a specific high-sensitivity IRMA (DYNOtest Tg-plus, BRAHMS Diagnostica GmbH, Berlin, Germany). Sera showing the presence of antibodies against hTG (AbhTG) or hTG-recovery less than 80% were excluded from the study. The receiver operator characteristic (ROC) curve analysis was performed to select the best cut-off levels, and diagnostic performance of the marker was evaluated. By using ONT4 cut-off level of 0.2 ng/ml and OFFT4 cut-off level of 0.5 ng/ml we obtained a sensitivity/specificity/accuracy profile of 0.92/0.98/0.97 and 0.97/0.98/0.98, respectively. We found false-negative results in three (12%) and one (4%) out of 24 patients with cervical recurrence by using 0.2 and 0.5 ng/ml cut-off levels, respectively. However, we found false-negative results in 13 (54%) and six (25%) patients when 1.0 ng/ml cut-off level was used. Finally, DYNOtest Tg-plus showed a very satisfactory intra- and inter-assay reproducibility in the very low hTG concentration range. Based on our data, we conclude that DYNOtest Tg-plus assay is effective and accurate in evaluation of patients with DTC.

Thyroid cancer

Four types of thyroid cancer comprise more than 98% of all thyroid malignancies. Papillary thyroid carcinoma (PTC) may have a very benign course while undifferentiated thyroid carcinoma (UTC) belongs to the most aggressive human malignancies. A variety of genes have been identified to be involved in the pathogenesis of thyroid carcinoma. Somatic Ras mutations seem to be an early event and are frequently found in follicular thyroid carcinomas. Somatic rearrangements of RET and TRK are almost exclusively found in PTC and may be found in early stages. Germline RET missense mutations lead to hereditary medullary thyroid carcinoma (MTC). In contrast, the significance of somatic RET mutations in sporadic MTC is unknown. p53 seems to play a crucial role in the dedifferentiation process of thyroid carcinoma. The precise role of PTEN remains to be elucidated. The only clearly identified exogenous factor that may lead to thyroid carcinoma (mainly PTC) is radiation. Of interest, radiation is capable to induce RET rearrangements. In general, early diagnosis is mandatory to enable the chance of cure. Surgery is the treatment of choice. Depending on the tumour type, surgery in combination with either radioiodine, external radiation or chemotherapy often enables the control of local tumour burden. In MTC and UTC, once thyroid cancer is spread to distant organs, efficacious therapeutic agents are almost non-existing. However, our growing knowledge of genes involved in thyroidal oncogenesis may contribute to the development of more effective treatment modalities. Some preliminary data on gene therapy are quite promising.